The Unique Lawrence (version 9)
THE
UNIQUE
LAWRENCE1
David G Rance
The ubiquitous and much maligned originators of the
“25¢ slide rule” are not all what they seem!
Why Lawrence?
It is easy to think that slide rule innovation and creativity in the 20th century was largely
the domain of commercial greats like Nestler, Faber-Castell, Keuffel & Esser, etc. But like
its maligned UK “counterpart” Unique, the ubiquitous Lawrence is wrongly and unfairly
just seen as a “pile ‘em high and sell ‘em cheap2” maker of slide rules.
Fig. 1: classic Lawrence 25¢ painted Enhanced Mannheim 10-B
In so many ways the American Lawrence Engineering Service was a kindred spirit of the
Unique Instrument Company of Brighton Ltd. Both makers had a charismatic founder
and a colourful company history. Bruce Babcock’s 1996 article in the Journal of the
Oughtred Society (JOS) recounted the Lawrence company history. This article covers
new and previously unreported revelations - the company’s European roots, bitter family
disputes, its unmatched cost control, the mystery behind the Lawrence model numbering
and the many innovative and highly inventive slide rules Lawrence made.
European roots!
George Lee Lawrence, the founder of the Lawrence family slide rule business was born
on 6th September, 1901. For many Europe-based collectors there is nothing more
quintessentially American than a Lawrence-made slide rule. But it may surprise
collectors on both sides of the Atlantic to learn that the Lawrence family are direct
descendants of John Philip Lorenz (1727-1800) who emigrated to the States from
Niederhausen, Prussia (now Western Germany) in 1748. So the company has traceable
European rather than exclusive American roots.
George’s father, George Raymond Lawrence (1868-1938), was born on his parents
LaSalle County farm in Ottawa and is the great-great-grandson of his Prussian ancestor.
A decade after marrying Alice nee Herendeen (1861-1930) in 1890, George senior
moved over 70 miles to Illinois’ largest city: Chicago. George Lee and his 10-year older
brother, Raymond Welcome, were both born in Chicago. In 1891 George senior opened
the Lawrence Portrait Studio. He went on to build the largest known camera and develop
an innovative process for flash photography. Later in life he started an aircraft company
with partner Harry Lewis: The Lawrence-Lewis Aeroplane Co. The company built biplanes
from 1913 to 1919. But he is best remembered as the world famous Chicago-based
pioneer photographer who took remarkable aerial pictures with cameras slung under
giant kites or large hydrogen-filled balloons.
Fig. 2: George Raymond Lawrence’s iconic aerial shot from 2000 feet of
San Francisco in ruins after the earthquake in May 1906
Lawrence “family” of companies
Like his UK counterpart, Burns Snodgrass (1881-1954) who founded Unique, Lee (he
never used George – favouring his middle name) became an entrepreneur. His education
was interrupted in 1909 when his mother Alice found out that his father had been having
an affair and soon after they split up. It was so acrimonious that claims and
counterclaims of kidnapping young Lee by both parents were first reported in the
Chicago Daily Tribune newspaper on 17th February 1911. It was still newsworthy a year
later when it featured in the Oakland Tribune in both the 31st March and 16th April
editions. The divorce became final in 1913. In the same year Lee’s father married Adele
nee Page (1894-1962). The timing of his parents’ bitter break-up might explain why
there is no record of Lee ever gaining a college degree.
His father’s success as a professional photographer and builder of biplanes was most
probably behind the two Chicago-based businesses Lee started around 1930. Sadly no
examples are known to have survived from the Lawrence Slide Rule Company. It made
and sold photography related slide rules/charts. But a second business, Lawrence
Airplane Models, flourished. The company sold a series of balsa wood kits of model
planes of “unusual flying ability” – see Fig. 3. The kits, with impressive wing spans of 24
inches or more, included replicas of popular aeroplanes of the day such as the Sopwith
Camel. The experience Lee gained cost-effectively manufacturing the many wooden
parts need for such kits may well have paved the way for his later successful second
attempt at manufacturing slide rules.
In 1935, five years after
starting
his
Chicago-based
businesses, Lee uprooted and
moved over 160 miles south
and out of state to Wabash,
Indiana. This move may have
been the result of an earlier
marital breakup. Lee married
the first of his eventual three
wives in 1922. She was Ada
nee
Zimmer
(1903-1975).
Within two years the marriage
was blessed with the birth of a
son, Lee junior (1924-2012).
Needless to say the marriage
did not last and by 1929 Ada
and her son had started a new
life in Philadelphia.
Fig. 3: Boxed (15½ x 3 x 1¼ inch) kit © 1931 for
building a “Fledgeling” – a model with a 24 inch
wingspan requiring no previous model building
experience
In Wabash Lee founded Lawrence Engineering Services to make and sell slide rules. By
now he was married to his second wife: Vivian nee Breyer (1915-1973). They met in
Chicago but were married in Indiana in 1934. But Vivian did not immediately move with
Lee to Wabash. She was ambitious and clever and, at first, may have been reluctant to
leave Chicago. When she did eventually join him she took an
active part in the business – particularly sales and promotion.
Mike Konshak’s “poster” succinctly summarises the
evolutionary path of the Lawrence slide rule. But unlike some
company success stories, this one revolves more around
marriage and divorce than technology!
Flourishing sales is the most likely reason that three years
after start-up the operation and the Lawrence family moved
13 miles west to larger premises in the neighbouring city of
Peru. This accounts for either a Wabash or a Peru provenance
being printed after the company name on all of their branded
slide rules. Apart from adding plastic veneers in the late
1950s, this is the start of the most innovative era of the
company. “PAT. PEND.” can be found on many of the
Wabash-made slide rules and on some later Peru-made
models. But no corresponding registered patent exists. Like
many other slide rule makers, Lee probably found it too timeconsuming and too costly to get full patent protection –
especially as the process involved annual renewal fees. It
was more cost effective to make a patent application to get
some initial protection and then let it lapse. However, apart
from those credited to 3rd parties, a whole series of
copyrighted designs are attributed to Lawrence Engineering
Services from the mid-1940s onwards – see Tables 1 and 3.
Fig. 4: Lawrence slide rules through the years3
Instigated by his second wife, Lee and Vivian were divorced in 1947. Vivian cited Miss
Louise Huber, an old family friend, as co-respondent in the action. Lee always fiercely
denied she was anything but a friend. But an inexplicable part of the divorce settlement
was that Lee “let” the slide rule business go to his ex-wife. Directly afterwards Vivian’s
soon to be new husband, the Rev. Frank Bozarth, became President of the company and
it was renamed: Engineering Instruments Inc. Twenty years later the business abruptly
folded after a major fire on July 5th 1967 burnt everything down. Despite being insured,
Frank Bozarth decided it was time to call it a day and the “Lawrence” family business
stopped trading after being in business for 37 years.
A year after his divorce from Vivian Lee remarried for the third and last time to divorcee
Nellie Donaldson nee Mowbray (1911-1990). They had met through the company as
Nellie had previously been the wife of the sales manager at Lawrence Engineering
Services. Having lost the slide rule business Lee threw his energies into a plastics
company he had founded in 1945: AGP Corporation. Lee’s initial interest in plastics
stems from the high breakage/waste rate in making and shipping Lawrence glass cursors
– especially the glass magnifying cursors for the DeLuxe version of the 10-B. Lee had
bought his own plastic moulding machines so he could replace glass magnifying cursors
with more durable and cheaper plastic versions. He clandestinely removed the machines
when he realised he was going to lose the slide rule business to his second wife. This is
borne out by no plastic magnifying cursor ever appearing on any of the models sold by
Engineering Services Inc. But Lee’s entrepreneurialism could not be dampened by family
strife. With the AGP Corporation he ended up as the OEM manufacturer for many highly
successful plastic toys. For example, the hit toy of the 1950s/1960s: “Etch-a-Sketch”. In
1963 he became part-owner of another Peru-based company: Precision Ceramics. He
died on 21st March, 1976 while on holiday with Nellie in the British Honduras. He is
buried at the Mount Hope Cemetery in Peru, Indiana. Fourteen years later Nellie was laid
to rest alongside him.
Fig. 5: August 5th 1960: Lee and Nellie at the opening of “Aerial Photography
1900-1910” - an exhibition of his late father’s work4
Lawrence standard “blanks”
Margins for the originator of the 25¢5 slide rule must have always been tight! In
“money-of-the-day”, a comparable retail price now would be no more than $4. Sadly
because of the fire in 1967 there is no way of knowing for sure the shop floor set-up and
working practices. However, after comparing over 50 different Lawrence/Engineering
Instruments slide rules, phenomenal cost-efficiency stands out. In his working life Lee
was considered a bit eccentric and short-tempered. But he was undoubtedly an “ideas
man” with a sound engineering brain. For example, he inexpensively rejigged the
working practices so that the company could go on to make many innovative slide rules.
This leveraged the company out of their “pile ‘em high and sell ‘em cheap” niche market.
If Lee was the “ideas man” it was Ed Snyder, a long-standing employee, who usually
turned them into something practical for the shop floor. It must have been soon after
they started manufacturing in Wabash, that they hit on the idea to use standard wooden
blanks. The company started by making two types of an 8-inch6 slide rule – a Mannheim
and an Enhanced Mannheim (but without the trigonometric scales). The scales were
printed in monochrome onto a solid frame wooden stock (see: Table 1). Later, for better
contrast, the front face and sometimes the back of the slide were first painted white
before the scales were added. Lawrence/Engineering Instruments ended up with an
eclectic mix of model sizes. The portfolio included stock lengths of 5, 6, 7½, 8, 8½, 9,
10, 10½ and 12-inches. However, despite the variety of stock lengths, certain unique
dimensions and characteristics never changed. Whether it was a Lawrence/Engineering
Instruments branded slide rule, a specially commissioned themed slide rule or even an
Original Equipment Maker (OEM) slide rule the:
width of the stock was always
1⅛ inch
thickness of the stock was always 5/16 inch
9
width of the slide was always
/16 inch
thickness of the slide was always ⅛ inch
top and bottom side edges (never bevelled) always had tracks for a onesize cursor – even if one was not needed
no scale was ever added to a side edge
the back of the stock was never painted
cursor (if needed) was always metal framed glass/plastic or all-plastic
(n.b. not all models came with or needed a cursor and for those that did come
with a cursor, more than often it broke or was lost)
On some models the slide was left longer than the stock. Conversion tables or
instructions were often printed on the back of the stock. Some even had a promotional
advert for a 3rd party on the back. But the unique tooling dimensions and characteristics
are always a sure-fire way of telling if a “look-alike” slide rule was made by
Lawrence/Engineering Instruments or by someone else.
The uniformity of the dimensions suggests all models were milled from standard 12-inch
solid frame blanks as the 10/10½-inch models were the most popular size. However, if a
single-sized 12-inch blank created too much wastage, they may have opted for several
different sized standard blanks – e.g. 12, 10/10½ and 6-inch6. To keep costs as low as
possible the wooden blanks were probably milled from the readily available and
inexpensive poplar trees - genus: Populas. However, not all the slide blanks were
interchangeable. Most Lawrence/Engineering Instruments models were simplex models
carrying no scales on the back of the slide. So for simpler rabbeting the rails along edges
of the slide are at the bottom. But some models did have scales on the back of the slide
(see Table 2). For such models the rails were naturally centred.
Lawrence/Engineering Instruments made many different models that carried the
company name – i.e. branded slide rules. But they made many more specially
commissioned themed and Original Equipment Manufacturer (OEM) slide rules. However,
identifying such unbranded slide rules can be tricky because the distinctive but
unpatented Lawrence style was often copied.
Lawrence/Engineering Instruments branded slide rules
Previously published Lawrence related articles felt there was no rhyme or reason to the
model numbering. Now having had the chance to examine first-hand almost all the
branded Lawrence slide rules ever made, I have found a way of making sense of the
cryptic model codes printed on the right-hand end of the slide. First it is important to
realise that all the slide rules carrying a Lawrence Engineering Services, Wabash/Peru or
Engineering Services Inc., Peru brand name belong to one of four distinct ranges:
1.
2.
3.
4.
Imperial range with n[n]-x[x] alphanumeric model no.’s
Metric range with nn[n]-x[x] alphanumeric model no.’s
Set & Book range
Plain range with no model no.’s
Most branded rules were part of the imperial range. The n[n] numerical prefix part of
the model number is the length of the stock in inches – hence the name: “imperial
range”. The first x alphabetical suffix is for all the different types within the range. The
optional extra last character [x] was for different versions of the same type.
Model #
Type/Name (© yyyy)
Cursor
Scale layout/Use
8-A
Mannheim
Yes
A/B,C/D
8-B
10-B &
DeLuxe
Enhanced Mannheim
Enhanced Mannheim
(DeLuxe only on the box)
Yes
Yes
Yes
A/B,CI,C/D,K but no S,L,T
A/B,CI,C/D,K but no S,L,T
DeLuxe version = magnifying cursor
10-C
ENGRAVER’S AND
PHOTOGRAPHER’S
PROPORTION CALCULATOR
LUMBER CALCULATOR
(© 1946)
No
For area % up & down scaling
(reduction/enlargement arrows point
to results - no cursor needed)
For lumber volume in board feet7
(set thickness & width, result on “D”
for given length – no cursor needed)
10-F
PRICING AND INVENTORY
RULE (versions © 1945 and
© 1946)
Yes
For discount or profit margin markup per gross/dozen/each in $’s and
value of stock in $’s
10-G
CUTTING SPEED
CALCULATOR (© 1946)
Yes
For recommended cutting speed in
f.p.m.8 for given drill speed & size
12-H
COPYFITTER
(© 1946 but credited to
Owen T. Taylor)
Yes
For font size and letter/word/line
spacing in points and picas9 when
typesetting (also version in Table 3)
10-I
MODEL BUILDER’S SLIDE
RULE (© 1947)
Yes
With the special tables on the back it
scaled down railroads/trains
10-D
10-Do
No
No
Model #
Type/Name (© yyyy)
Cursor
Scale layout/Use
according to various railway gauge
sizes to make replica size models
12-J
PRO-RATER (© 1948)
Yes
For calculating days between two
dates and the pro-rata premium for
a given number of days (pro-rata
table to four decimal places on back)
9-K
MUSIC TRANSPOSER10
(© 1947)
No
For constructing chords in any key &
transposing one key to any other
(red/blue dots – no cursor needed)
8-L
COPPER WIRE SELECTOR
“Voltage Drop Calculator”
(© 1946)
No
For minimum wire size in A.W.G.11
(set length & load, result on “D” for
440/220/110 voltage drop – no
cursor needed)
10-N
Yes
6-Op
PRINTER’S PROPORTION
RULE (© 1946)
FLASHRULE (© 1946)
6-Ow
FLASHRULE (© 1946)
No
For moving between inches & picas9
when printing/publishing
For correct lens aperture per type of
GE or Westinghouse flashbulbs.
Ditto but for WABASH flashbulbs
(set film speed & lamp, result on “D”
for distance – no cursor needed)
No
Table 1: Imperial range of Lawrence/Engineering Instruments branded models
As shown in the Appendix-A picture gallery, apart from the “everlasting” model 10-B,
this range came out long before the Engineering Instruments Inc. era. But it remains a
mystery why two letters in the model sequence were skipped – e.g. why has no type E
or M ever turned up? Maybe they were prototypes that never made it to market.
The idea for the metric range came from fellow collector David Green. With one dubious
exception, it covers all Lawrence/Engineering Instruments branded slide rules with
model numbers that do not conform to the syntax of the imperial range. This time the
nn[n] numerical prefix part of the model number refers to the length of the “D scale”12
in millimetres rather than the length of the stock in inches - i.e. 250mm. Therefore the
name: “metric range”. The x[x] alphabetical suffix cryptically depicts the different types
in the range. “BT” may stand for a model B from the imperial range and the T for the
three extra trigonometric scales on the back of the slide. Likewise “V” may stand for
veneered scales. The A on the “77A” could correspond to the name on the slide rule:
“American Log-Log.”
Model #
Type/Name (© yyyy)
Cursor
250-BT
Enhanced Mannheim
Yes
250-V
Enhanced Mannheim
Yes
Scale layout/Construction
A/B,CI,C/D,K//S,L,T
Front face and back of slide
lacquered/painted
A/B,CI,C/D,K//S,L,T
Front face and back of slide
veneered with hard white plastic
Model #
Type/Name (© yyyy)
77A
Log-Log Decimal Trig
Cursor
Scale layout/Construction
Yes
LL02,LL03,DF/CF,CIF,CI,C/D,LL3,LL2
//LL01,K,A/B,T,ST,S/D,L,LL1
Duplex all plastic (? OEM made rule)
Table 2: Metric range of Lawrence/Engineering Instruments branded models
Now the back of the slide was also part of the scale layout, a small clear plastic insert
was added into well of the stock at the righthand end. With the hairline in the insert it was
possible to set or read off results from using the
trigonometric scales without having to reverse
the slide. Also on many, but inexplicably not all
250-BT’s, there is another 3-digit number printed
under the slide on the left-hand end.
Speculatively this might have been a batch or
production-run number. The models in the metric
range predominantly come from the post Lee
Lawrence Engineering Services Inc., Peru era –
see the Appendix-A picture gallery.
As shown by the only company-issued flyer I
have ever been able to find, by the late 1950s
more internationally orientated marketing and
printing the scales on white plastic veneers to
increase legibility were now part of the business
philosophy.
Fig. 6: Front page of a 4-page marketing flyer from ca. 1958
By now the $2.00 250-V was the top end model with the $1.25 250-BT their “Students
Special” and the old faithful 10-B reduced to being their 60¢ budget slide rule. Being all
plastic, duplex and not conforming to the unique dimensions and characteristics of all
Lawrence/Engineering Instruments made slide rules, the 77A is an oddity. It is,
suspiciously, identical with the Acu-Math model 150 Duplex Log Log Deci Trig slide rule. I
believe the 77A is an OEM slide rule made by Acu-Math for Engineering Instruments Inc.
The front cover of the flyer also boasts two circular slide rule made of “vinylite”. Clearly
by this time Engineering Instruments Inc.
resold all-plastic slide rules and a wide
assortment of drawing instruments – none
of which they could have made in-house.
The set and book range shows how Lee
forged new partnerships with other
companies. Copyrighted in 1939 Lee first
came up with the novel idea of marketing a
toy: the Lawrence Secret Code-Maker.
Fig. 7: Code-Maker boxed set
The boxed set contained two (i.e. also one for your “best mate”) identical 7½-inch
Secret Code-Maker slide rules without cursors and a 16-page “Make Your Own Secret
Codes in a Flash” instruction booklet. From the image on the box it was aimed at
teenagers but intriguingly the image on the instruction booklet is of an adult. Perhaps
Lee was trying to play to both the childhood “secret agent” fantasy and the prevailing
WWII adult nervousness about secrecy? The A-Z, inverted Z-A and 5-cycle 0-9 scales
make it easy to create or decode a Vigenère cipher13. This is a method of encrypting text
messages with a simple one-step substitution, reversed substitution, mixed substitution
or a more complex transposition code using a mixture of substitution methods. The
Lawrence booklet incorporates and greatly extends a pamphlet written by W. St. John
Maloney14 and copyrighted by the Cole Corporation of Chicago in 1939. Unlike other
Lawrence slide rule guides15, this booklet is much more educational – including many
code-related historical facts going back as far as the days of Julius Caesar. There were at
least two variants of the code-maker. One was called: The BEICH Secret Code-Maker.
This was an 8-inch6 Lawrence branded rule with a thin metal “fisheye” cursor and a
simplified 4-page leaflet. It was part of a loyalty scheme and could be won by collecting
Beich Whiz16 chocolate bar wrappers. So Lee was doing a “Willy Wonka” decades before
Roald Dahl published “Charlie and the Chocolate Factory” in 1964 and Gene Wilder
starred in the 1971 film of the book. The other version was the 6-inch6 Dick Tracy CodeMaker. Like the original 7½-inch6 model, the Dick Tracy version had no cursor. It came
with a Dick Tracy emblazed simplified 4-page version of the booklet and was presumably
marketed in cooperation with the “Chicago Tribune New York News Syndicate”, the
publishers of the comic strip book hero created by Chester Gould (1900-1985).
Fig. 8: 8-inch Beich and 6-inch Dick Tracy “Code-Maker’s”
In 1942 the Austin Publishing Company copyrighted an idea for a “teach yourself”
workbook on how to use a slide rule. The US Letter sized hard-backed book came with a
Lawrence DeLuxe (magnifying cursor) 10-B slide rule. The authors were Hobart H.
Sommers, Harry Drell and T.W. Wallschlaeger and it was published by two companies.
The Grosset & Dunlap version had a dirty orange and black cover and was published in
New York (208 pages incl. Tables of Logarithms, Trigonometric Functions of Angles and
the Answers). The Wilcox & Follett Co. edition had a dark-green and gold cover and was
published in Chicago (same 208 pages but with an extra loose-leaf Answers addendum).
Much later, in 1961, Lakeside Toys brought out a Draft-a-Plan Kit™. This large boxed
drafting set came with a plastic electric-powered
drawing slope, many drafting related aids and an
Engineering Instruments Inc. made “5-B” pocket
Enhanced Mannheim slide rule. The “Drafting is
Fun” guidebook has a chapter on how to use the
slide rule. Finally, in 1966, the Cadillac Publishing
Company started publishing a 33-volume (7¼ x
10½ inch) Self-Teaching Encyclopedia. Volume 1
was “Mathematics Made Simple” and the publishers
proudly sold it with a “free” model 10-B slide rule.
Later, despite all the illustrated examples being
based on the model 10-B, the company replaced it
with a shorter (and cheaper) 6-inch6 version.
Fig. 9: Lakeside Draft-a-Plan Kit™ set for a teenager
The final plain range of branded slide rules is chronologically probably some of the last
wood/painted slide rules Lawrence/Engineering Instruments sold. Apart from coming
from the Peru factory, I can think of no good reason for leaving off a model number on
any branded slide rule. Almost without exception, one did have “10-BK” on the box, all
the branded slide rules without a model number are identical with one of the classic
models – the 10-B or the later 250-BT. Maybe the model number was left off to give the
slide rules fashionable cleaner lines for the “swinging sixties”. An example is part of the
Appendix-A picture gallery.
Lawrence/Engineering Instruments specially commissioned themed slide rules
Nearly all are unbranded and have no model number. Most have non-conventional scale
layouts and are so innovative that almost all the designs were copyrighted. They came in
various sizes (occasionally different sizes of the same model) and most, but not all, had
a cursor.
It is easy to mistake many unbranded themed slide rule as being made by
Lawrence/Engineering Instruments. But many are just “look-alikes” - similar in style but
made by someone else. The listed examples all conform to the unique dimensions and
characteristics of a Lawrence-made rule. However, any named model could easily have
been commissioned by more companies/parties than those listed in the table.
Commissioned by (© yyyy)
Size6
Lakeside Toys – Draft-A-Plan,
Minneapolis (© 1961)
5"
Students Learner pocket slide rule –
Enhanced Mannheim (“5-B” on box) with
A/B,CI,C/D,K but no S,L,T
B.F. Grizzle, Washington and
Terre Haute (8" version © 1941,
12" version © 1945)
B.F. Grizzle, Washington and
Terre Haute (© 1941)
8"
&
12"
8"
Gas Pipe Line Slide Rule for calculating
the gas flow capacity/hour through a pipe
of a given diameter
Gas Displacement Meter Calculator for
calculating gas rates through displacement
meters @ various pressures
Model Name/Use
Commissioned by (© yyyy)
Size6
Model Name/Use
B.F. Grizzle, Washington
(© 1941)
8"
Gas Low Pressure Line Flow Capacity
Slide Rule for calculating the pressure
drops for a given line flow & gas line size
needed to deliver a given amount of gas
B.F. Grizzle, Washington
(© 1944)
8"
B.F. Grizzle, Washington
(© 1939)
8"
Pipe Open Flow Capacity Slide Rule for
calculating open flow rates based on pilot
tube pressure readings
Pipe Orifice Meter Calculating Rule for
calculating the size of conduit/restriction
needed to create a required pressure drop
B.F. Grizzle, Washington
(© 1944)
8"
Madison Manufacturing
Company, Michigan (© 1947)
8"
Thomas Specialities, California
(© 1948)
8½"
Music Transposition for composing,
transposing or creating harmonies
Massachusetts Institute of
Technology (MIT), Cambridge
Radiation Laboratory – c1941
Roy C. Spencer
10"
Antenna Slide Rule (confidential and
classified) for calculating radar antenna
beam patterns - beam width, gain, etc.
Massachusetts Institute of
Technology (MIT), Cambridge
High Voltage Laboratory – 1943
W.W. Buechener & E.A. Burrill Jr.
C.V. Ore, Illinois (© 1955)
(n.b.: Acu-Rule made an OEM
plastic version of this rule)
10"
Exposure Slide Rule (possibly for the US
Navy in WWII) for calculating exposure
times of super high-voltage steel
penetrating X-rays of castings & munitions
The S-M Slide Rule (DS/CI,C/D/DM) a
Simplified Multi-purpose type of Enhanced
Mannheim teaching rule supposedly making
it easier to learn how to multiply/divide, etc
Canadian Radium & Uranium
Corp., New York (© 1942)
10"
Gamma-Ray Radiographic slide rule for
commercial (steel) rather than medical use
Miller Motor Company, Illinois
(© 1950)
10"
Air and Hydraulic Calculator
(DIA,A/B,CI,C/D,GAL) for calculating flow
rates through different sized pipes
Fun Incorporated, Illinois &
Ideas Unlimited, California
(© 1950)
6"
&
10"
Poker Meter for 5/7 card stud or 5 card
draw poker. Based on number and value of
cards held, a colour code recommends the
best play – “Get Out”, “Stay” or “Raise”
PIC Walsh Freight Co. &
Plaza Express Company Inc.
(© 1939 M.T. Brockman)
9½"
Traffic Manager's Slide Rule for checking
freight shipping charges or shipping rates
or shipping truck/carload breaking points
and calculating storage costs
US Army (DeYOE)
10"
Artillery Range Finding (“Graphic Table”)
for calculating how many guns and how
many rounds of high explosive shells are
10"
Water Line Capacity Slide Rule for
calculating the friction loss in a section of
pipe & head loss for a given pipe diameter,
length & flow
Madison Speed Calculator for calculating
drill & cutting speed for a given diameter
Commissioned by (© yyyy)
Size6
Model Name/Use
needed to be sure of hitting a target
Murphy & Murphy Inc., Texas
& Caprock Materials Co., Texas
& Warren E. Fennell, Indiana
Tokheim Corporation, Indiana
(© 1948)
10½"
Tenbrook Enterprises, Indiana
12"
L.P. Gas – for calculating the temperature
correction (°F) needed when making bulk
deliveries of propane
L.E. Waddington, (© 1947)
12"
Music & Music Acoustics for transposing
chords, interval ratios, harmonic series,
octaves and frequencies
Taylor Publishing Co, Ohio (©
1946 credited to Owen T. Taylor)
12"
Copyfitter for font size and
letter/word/line spacing in points and picas9
when typesetting (copy of the 12-H)
United States Aviation
Underwriters Inc.,
(© 1944 Albert J. Smith)
12"
Underwriters slide rule for calculating
the risk duration (in days) for aviation
related ventures (table on back has
cancellation ratio’s/days)
Pioneer (address unknown) &
Adler Communications
Laboratories, New York
(© 1952 J.B. Epperson)
12"
Epperson TV Coverage Calculator for
calculating VHF and UHF signal coverage
based on a signal strength, FCC
propagation curves and antenna height
(UV/M and DB conversion table on back)
Radio Corporation of America
(RCA), New Jersey
12"
F.M. COVERAGE CALCULATOR for
estimating (according to FCC propagation
curves) coverage of FM radio stations
according to the type of RCA radio antenna
12"
Concrete Quantity Calculator for
calculating cubic yards of concrete needed
for or in a wall of certain dimensions
“K” Factor – using high & low outdoor
temperatures and gallons of household fuel
oil left, the K factor = days of supply left
Table 3: Lawrence/Engineering Instruments unbranded
specially commissioned themed slide rules
As shown by the Poker Meter, Traffic Manager's Slide Rule and the Concrete Quantity
Calculator entries, different companies often commissioned different sizes or different
versions of the same themed slide rule. So this series proves, yet again, how
Lawrence/Engineering Instruments successfully used their standard blanks to make an
enormous variety of interesting and ground-breaking slide rules – often (re)selling the
same design to multiple clients. An example of all the listed models can be found in the
Appendix-B picture gallery.
Lawrence/Engineering Instruments OEM slide rules
By its nature this section is subjective and, in part, controversial. Lawrence/Engineering
Instruments made OEM slide rules are, by definition, unbranded although some do have
recognisable model numbers. One of the more easily made mistakes is to confuse them
with certain early models from the St. Louis based Festus/Acu-Rule Mfg. Co. - in
particular their model 10-D. Because of the model numbering it is often mistaken for a
Lawrence/Engineering Instruments 10-B. They are similar in size, have the same solid
frame wooden construction and the same scale layout - an Enhanced Mannheim without
the trigonometric S,L,T scales. But the telltale difference is that the Acu-Rule 10-D has a
bevelled top edge inch scale – a feature never used on any Lawrence/Engineering
Instruments slide rule.
Over the years it has been speculated that the budget-range models of some American
commercial slide rule greats are OEM slide rules made by Lawrence/Engineering
Instruments. The favourite nominations are:
Keuffel & Esser
DIETZGEN
POST
Charvoz-Roos
A. Lietz Company
model: N4058W
models: 1767/68/69P
model: 1446-D
model: SR-31
model: 2974N
All are Enhanced Mannheim’s and all are “Lawrence-like”. But only the Charvoz-Roos
SR-31 and the Lietz 2974N are OEM rules from Lawrence/Engineering Instruments both rebadged 250-BT’s. The main OEM customers were businesses, government bodies
and resellers of scientific or office/drawing equipment.
Made for:
Rebadged
DUPONT - Neoprene, Rubber
Chemicals and Colors, Delaware
250-BT
U.S. Navy
250-BT
DU MONT, Ohio
250-BT
8-B
Burger Scientific Supplies, Boston
250-BT
W. M. Welch Scientific Company, Illinois
NOBEMA Products Corp., New York
250-BT
250-V
10-B
10-B
PAULL INSTRUMENTS
10-B
LARCH, New York
10-B
Coyne Electrical School, Chicago
10-B
GENE LOEWY PRODUCTS, New York
ANCO PRODUCTS Co., Ohio
10-B
8-B
Table 4: Lawrence/Engineering Instruments “rebranded” OEM slide rules
As in the past businesses often used such OEM slide rules as promotional gifts, many
more unlisted examples undoubtedly exist. Nevertheless the listed examples do show
how Lawrence/Engineering Instruments found yet another successful avenue to
reuse/rebrand their popular Enhanced Mannheim and Mannheim type slide rules. The
Charvoz-Roos, the Lietz and some of the examples listed in the table are part of the
Appendix-B picture gallery.
Just toys or calculating aids for professionals?
The two most well-known models, the 10-B and the 250-BT, were their flagship “pile ‘em
high and sell ‘em cheap” slide rules for everyday/school use and the budget market. But
most of the other Lawrence/Engineering Instruments branded slide rules from the
imperial range and all the specially commissioned themed slide rules are superb
examples of innovation and inventiveness. But who were the target customers?
The Secret Code-Maker series and the 5-inch6 pocket slide rule in the Draft-a-Plan Kit
were aimed at the teenager/toy market. The hobby market was the most likely target for
the 10-I (MODEL BUILDER’S) and the 6-Op/w (FLASHRULE) models. The remaining
models from the imperial range and nearly all the specially commissioned themed slide
rules had a serious use and could have easily found their way into a tradesman’s toolbox
or onto a professional’s desk. But the most convincing examples are the WWII war effort
related specially commissioned Antenna and Exposure slide rules made for MIT. The
design of the Antenna Slide Rule for calculating radar antenna beam patterns being
considered so strategically important that both the British and American governments
had it classified and kept it classified long after WWII had finished.
Slide rules from Lawrence/Engineering Instruments are often ridiculed because of their
cheapness and basic construction. But perhaps without realising their provenance, many
were used and appreciated by professionals from many, many trades and professions.
The Lawrence legacy
Family acrimony was the reason why “Lawrence” was purged from the company name
after 1947. However, Lee Lawrence was the charismatic inspiration for the company’s
most inspired 1935-1947 era and the reason for the company’s success and longevity.
It is certainly true that all Lawrence/Engineering Instruments slide rules were cheaply
made when compared with the likes of K&E, Pickett & Eckel, Faber-Castell, Nestler, etc.
They also probably never made it on to NASA’s shortlist for slide rules to go on five of
the Apollo missions. But this is like expecting an OPEL/General Motors family saloon to
be built to the same engineering standards and build quality as a Mercedes-Benz S-class.
So when only accuracy to a couple of decimal places was needed, Lawrence/Engineering
Instruments produced fit-for-purpose slide rules for a price that no other manufacturer
matched. Their low-cost was a unique advantage allowing the company to develop an
impressive range of slide rules for the professional, hobby, toy and budget markets.
Unenlightened slide rules collectors may dismiss Lawrence/Engineering Instruments slide
rules as "uninteresting" and not worth bothering with. In reality their esteemed peers
could not match their low-cost business model and their ability to continually find new
partners and avenues for new innovative slide rules. In the post Lee Lawrence years by
moving to plastic veneered scales for the model 250-V shows Engineering Instruments
Inc. wanted to embrace technological improvements. But this meant the 250-V ended up
retailing for three times more than the original painted 10-B they were still selling.
Like Unique, Lawrence/Engineering Instruments slide rules are often maligned but for a
modest investment any determined collector can find some amazing and colourful
models that would certainly grace any slide rule collection. The Lawrence legacy is
undoubtedly an unsurpassed portfolio of surprisingly innovative and inventive slide rules
rightly earning it the accolade of: “The Unique (Lee) Lawrence”.
Acknowledgements
Without help this story would have been, at best, hopelessly incomplete. I need to
thank:
Richard Rose: for donating many Lawrence rules to my collection and unselfishly
acting as “my agent for all things Lawrence” in the States,
Bruce Babcock: for sharing his detailed Lawrence/Engineering Instruments
knowledge and for images from his impressive Lawrence collection,
Mike Konshak/ISRM: for images and permission to use the Lawrence related
information from his ISRM website,
David Green: for providing the crucial tip that enabled me to unravel the coding
of the Lawrence model numbering,
George Keane: for information on the Festus MFG and AcuRule MFG companies
and how their slide rules relate to Lawrence,
Sandra Bird: for information relating to the Lawrence family and company,
Tom Dilatush: for encouragement and helpful suggestions,
Peter Hopp: for information on Lawrence slide rules sold in the UK and images,
Cyron T. Lawson: for information on his Lawrence collection,
Paul J. Tarantolo Jr.: for information and images of his Lawrence collection,
Michael Frey & Philip Stanley: for providing two previously unseen models,
Deborah Douglas: for information and images from the MIT Museum.
A special postscript mention should go to Louis Block. While researching his family
history he discovered that his maternal grandmother, Ada Verbit nee Zimmer, was Lee
Lawrence’s first wife. This led him to my article. In late 2016 he contacted me. With the
information he kindly shared I could correct and supplement aspects of the convoluted
Lawrence family history as part of a major update to this article in 2017.
Bibliography
1. Hems, Ray: “Unique’ Unique’s”, Proceedings of the 8th International. Meeting of
Slide Rule Collectors, United Kingdom, October, 2002, Pg. 69.
2. Babcock, Bruce: “Lawrence Engineering Service – A Tale from an American
Small Town”, JOS Vol. 5, No. 2, October, ISSN 1061-6292, $12.00, 1996, Pg. 55.
3. Hopp/Barnes/Green: “Letters to the Editor”, JOS Vol. 6, No. 1, March, ISSN
1061-6292, $12.00, 1997, Pg. 49.
4. Chicago History Museum (CHM): Department of Rights and Reproductions http://www.chicagohs.org/ .
5. International Slide Museum (ISRM): a museum dedicated to the students,
educators, scientists and engineers of the past and those still present, and to
promote the lost art of numeracy - www.sliderulemuseum.com/ .
6. Engineering Instruments Inc.: Factory and General Office supplies catalogue,
4 pages, ca. 1958.
7. W.M. Welch: Scientific apparatus and supplies catalogue, 1959.
8. Berger Scientific Supplies: catalogue B, 1958.
9. Family Search: new official genealogy website of The Church of Jesus Christ of
Latter-day Saints - www.familysearch.org/ .
10. Random Acts of Genealogical Kindness: Internet based organisation of
volunteers established in 1999, www.raogk.org/ .
11. Find A Grave: a website for: (i) registering graves, (ii) recording memorials or
tributes and (iii) genealogical information - www.findagrave.com/index.html .
12. ProQuest Historical Newspapers: Chicago Daily Tribune (1872-1922) February
17th, 1911.
13. Family Link: newspaper archive for the Oakland Tribune www.familylink.com/stream .
14. Wikipedia Foundation: online free encyclopedia - www.wikipedia.org/ .
15. Massachusetts Institute of Technology/MIT Museum: exhibition “The Most
Important Instrument: Slide Rules and the Making of the Modern World”
- http://web.mit.edu/museum/exhibitions/sliderules.html .
16. Guerlac, Henry C: “Radar in World War II” Vo