Slide Rule Dates and Time-Lines

Aids in Determining the Age of Your Slide Rule

1909 - Copyright Act on published works passed by Congress. COPYRIGHT XXXX and © XXXX
1943 - 2 digit Postal Zone codes to increase efficiency of delivery because of a wartime shortage of staff. Example: St. Louis 12, Missouri.
1951 - 3 digit Area Codes in Phone numbers implemented by AT&T (Developed in 1947).
1963 - The use of 5 digit Postal Zip Codes in USA addresses adopted but not mandantory.
1963 - The change from state abbreviations to two letter codes (Colo. to CO, Ill. to IL)
1967 - The use of 5 digit Postal Zip Codes in USA addresses now mandantory.
1983 - The use of Zip+4 Postal Zip Codes began used by USPS

---

Estimating Dietzgen Slide Rule Dates

The downloadable charts are a matrix of Dietzgen slide rules, catalogs and price lists that was compliled by Bruce Babcock, Ph.D. and was published in the Journal of the Oughtred Society (JOS) October 1996, Volume 5, Number 2. This comprehensive research will enable you to find the period of manufacture for most every Dietzgen slide rule from 1887 through 1972. Combined Large 6.47MB

---

Estimating K&E Slide Rule Dates

Most Keufel & Esser slide rules had serial numbers, but unfortunately they reused their 6-digit serial numbers several times. This chart was developed by Ed Chamberlain to help determine the date of manufacture, but one must first zero in on which period the slide rule was made. Look at catalog's in the museum library and visit Clark McCoy's: Dating K&E Slide Rules

Here are some excerpts written by Clark McCoy: Serial Numbers: Serial numbers started in 1924 beginning with 0 and going through 999999 then rolling over to 0 again. There were three rollovers occurring in 1943-1944, 1954, and 1962. In general the production rate was about 70,000 rules per year until the 1950s. In the 1950s and it was over 100,000 per year. The 1960s had a production rate of about 100,000 per year for several years and tapering off in the 1970s ending at about 700000. In general it is safe to assume a linear production rate between the rollover dates particularly for the common types rules. Serial numbers can be used to approximate the manufacture date of a given rule however not necessarily the sales date. The common rules were produced in regular batches but the specialty rules did not sell as well and a given batch of rules might stretch over several years. It is not uncommon to find rules in the 1960s in 68 xxxx series packaging but 4000 series model numbers on the rules. The Fuller and Thacher's slide rules had their own serial number systems.

Model Numbers: There were four different number series in the history of the slide rule line. 1881-1883 -The numbers 479-481 were used. 1887-1899 -The numbers 1740-1749 were used. There was little if no logic to these numbers. 1900-1961 -The numbers 4000-4199 were used. There were logical groupings of numbers and dash numbers were used to depict length variations of a given rule type. "N" was used as a prefix many times to denote some change in a given model. The use of the "N" prefix is not always consistent. Removal of the "N" prefix also indicated a variation in the model. 1962-1975 -The numbers were converted to a 68-xxxx number series. The dash number scheme for length variations was abandoned. There are numerous examples of 68 xxxx series numbers on retail boxes and the slide rule inside has the old 4000 series number on it. We are sure that this was in the early 1960s while they were working through old 4000 series stock.

Cursor Types: The cursors used on K&E slide rules evolved over the years. When they changed, all production of all models was switched over.There is a definite timeline to the cursor models. Before 1906 - Slide rules either had no cursor, a brass chisel type cursor, or a metal framed glass cursor. 1913-1915 - A complex cursor that has been named the "column cursor" was introduced for duplex rules. 1915 - All slide rules were fitted with an all glass cursor. The first issue had metal end blocks. 1916-1933 - The metal cursor cursor blocks on the all glass cursor were replaced with plastic ones. 1933-1935 - The plastic cursor blocks were modified to have flanges to cover the edge of the glass. 1936- mid 1950s - The "improved cursor" with a metal rim around the glass was introduced. mid 1950s-1975 - The glass cursor lenses are replaced with molded plastic ones.

---

Time Line for Frederick Post - POST - Teledyne-Post

Post sold a wide variety of slide rules, both under its own name and under the names of various manufacturers. Post itself actually made no slide rules; even those rules that bore the Post brand name were manufactured by others. At one time or another Post brand slide rules were made by Dennert & Pape, Nestler, Faber, Hemmi, Lawrence Engineering Service, Charvoz-Roos, Bruning and Gilson. Post also sold branded slide rules from Richardson, Vicari, Boucher, Sexton, Halden, Chandler, Ritow and Winslow. c1890 - Frederick Post founded in Chicago to manufacture and sell drafting, engineering and surveying supplies. up to 1932 - Post slide rules were made by German manufacturers Dennert & Pape, Nestler and Faber. 1932 - Post began buying all of its straight slide rules from Hemmi Keisanjaku in Japan. 1932-1941 - Hemmi-manufactured rules have no date code and are marked "Made in Japan" 1941-1946 - WWII. Post buys slide rules from Lawrence Engineering Service, Charvoz-Roos, Bruning and Gilson. All Post slide rules with "Made in USA" come from this period. 1944 - The word 'POST' surrounded by an ellipse becomes the permanent logo. 1946-1950 - Post resumes rebranding Hemmi slide rules, rules marked "Made in Occupied Japan". 1950 - Two character date codes appear (see Hemmi date codes). 1951 - Hemmi drops the "Occupied" and marks slide rules "Made in Japan" or just "Japan". 1951 - Hemmi creates the Post Versatrig (1450) and Versalog (1460) Slide rule exclusivly for the North American Market. 1957 - Success of the Versalog prompts Hemmi to make pocket versions, the Post pocket Versatrig (1451) and Versalog (1461). 1970 - Post becomes Teledyne Post in 1970, slide rules sold under both the Post and Teledyne Post names. 1972 - The Frederick Post brand name disappeared and the Teledyne Post '44' numbering system was introduced. c1975 - Teledyne Post ceases selling slide rules. The date code (see Hemmi) is in the form 'HF' where the first letter identifies the year according to the system 1951 = B, 1952 = C, 1953 = D, etc., and the second letter identifies the month according to the scheme A = January, B = February, C = March, etc. Thus, 'HF' indicates a slide rule made in June 1957. Hemmi continued with this dating system until the end of production.

Frederick Post Logos from 1903-1975

---

Relay, Ricoh and re-branded variants

1951 - Post war Japanese manufacturer Nippon Slide Rule founded, and begins manufacturing of Nikkei slide rules, later using the brand name of Relay, selling to US markets as Relay Industrial Co. 19?? - Japanese Corporate name changed to San-Ai Kekki Ltd. April 1, 1963 - San-Ai Kekki Ltd. joins along with Riken Optical Co. and becoming part of a large conglomerate, now named Ricoh Ltd., which includes Coca-Cola distribution in Japan. 1977 - Slide Rule productions ceases. Today - Ricoh is a major manufacturer of office equipment. Relay/Ricoh supplied slide rules to US and European distributers and rebranded the slide rules for US and Canadian companies with names such as: Alpha, Alvin, Charvoz-Roos, Compass, Dietzgen, Eagle, Engineers, Jason, Lafayette, Lietz, Tobe, Lutz, Fuji, Micronta, Omega, Paleo, Pickett (the B1 only), Relay, Ricoh, Sans & Streiffe, SIC (Scientific Instruments Co), Skyline, SELSI, Staedtler-Mars, J.C.Penny, and Wallace & Wallace. Many Relay/Ricoh manufactured slide rules have date codes stamped into the body of the stock. They take the form of two letters, followed by a number, such as  K.K-1, J.K-1, H.K-3, E.K-5, etc. The first letter is the year, as is listed in the following table. The second letter, restricted to either S or K is assumed to be the manufacturing location. Today, Ricoh is known to have factories in the Shizuoka and Kanagawa prefectures, but at the time The significance of the number is unknown, the highest found in existing collections is 6. It could simply be a batch number.

Relay/Ricoh Date Code Locations

1894 - It is believed that the slide rule first came to Japan when Dr. Ritaro Hirota and Toragoro Kondo, the latter as the Head of the Construction Section of the Internal Affairs Ministry, visit the US and Europe, and bring a Mannheim slide rule back with them from France.
1895 - Jiro Hemmi, was working as a scale divider at the time, began research into manufacturing slide rules, this representing the beginnings of slide rule manufacturing in Japan.
1912 - The basis for founding Hemmi Slide Rule was established. As a result of a study made of materials, bamboo indigenous to Asia, was selected as the material, resulting in the granting of patents for a bamboo slide rule not only in Japan, but in England and France in 1920, and in the US, China, and Canada in 1920.
1917 - In December, the SUN mark is established as the Hemmi trademark. Being the symbol of Japan itself, the image of the rising sun was thought to bode well for the future of the firm's business.
1923 - Jiro Hemmi proposed a unique mechanical cutting method that enabled the achievement of excellent scale accuracy, and succeeded in mass production with uniform quality, this achievement winning wide acclaim.
1925 - Hisashi Ohkura, later to be president of Hemmi, joined the management team and succeeded in actively promoting export sales.
1928 - In April, the joint capital company Hemmi Seisakusho is established.
1929 - The invention of the non-logarithmic P and Q scales by Drs. Sadatoshi Betsumiya and Jisuke Miyazaki was applied to the Japan's first duplex slide rule, which was sold under the model name of Universal, this product winning wide acclaim.
1933 - In July, Hemmi Seisakusho was reorganized as a stock company, with a capital of 300,000 yen.
1935 - Director Shinzaburo Ohno was sent to the US and Canada to develop marketing channels overseas. In December, capital was increased to 500,000 yen, this to be increased further to 750,000 yen in 1940.
1938 - One-time research department head Eimei Hirano proposed the trig function SI and TI scales.
1940 - The main production facility was constructed in Shirako in Saitama Prefecture, hereafter to be called the Shirako Factory, on a plot of approximately 40,000 square meters (approximately 425,000 square feet). Jiro Hemmi was honored by receipt of a government award on the occasion of the 2600th anniversary of the legendary ascension of the Emperor Jimmu to the throne.
1943 - Hemmi Seisakusho constructs its Matsuyama Factory. Slide rules are used in Japanese middle school textbooks for the first time.
1945 - The Chichibu Factory is constructed, and production levels increase sharply.
1946 - The company name is changed to Hemmi Keisanjaku KK (Hemmi Slide Rule).
1950-51 - The Versalog slide rule is jointly developed with the Frederick Post company in the US. Standard duplex slide rules are redesigned as the new models 250, 255, 256, and 259, aimed at the US market. The slide rule is again made a compulsory part of the curriculum in middle schools.
1952 - Jiro Hemmi is honored by receiving a government award. The first edition of Keisanjaku Report (Slide Rule Report) is issued as the official publication of Hemmi Slide Rule.
August, 1952 - The manager of the Shirako Factory is sent to the US to interact closely with Frederick Post, the Hemmi representative, in research.
November, 1952 - The Tokyo Chamber of Commerce holds the first Slide Rule Competition, an event which is to be held once each year.
1953 - Jiro Hemmi dies, and is posthumously presented by the government with an award for his achievements.
August, 1954 - The president of Richardson & Company, the Hemmi Hong Kong representative visited Japan to discuss expanding the business.
1954 - In October, Alfred F. Kunz of Siber Hegner Co., Ltd., Zurich, the Hemmi representative in Switzerland visits Japan to discuss, among other things, methods of promoting the slide rule.
1954 - The Japan Chamber of Commerce establishes the Slide Rule Skill Certification Examination system, the first examination being held in November. The Chamber, with the backing of the Ministry of Education, holds its first open paper contest, inviting papers from middle school teachers on the theme of their methods of teaching the use of the slide rule.
1954 - Director Ohkura becomes a managing director.
1955 - Director Norio Matsumoto becomes the head of the Shirako Factory. Improvements are made in both quality and production levels. A proposed new two-story factory building, with environmental control (reinforced concrete construction) is built (approximately 1400 square meters (15,000 square feet)).
November, 1954 - R. J. Piehl, president of Frederick Post Co., visits Japan to discuss a plan for expanded business.
1956 - The 60th anniversary of founding is held, with awards given to personnel who had made contributions related to the slide rule. Developmental History of the Slide Rule is published to mark this event.
1956 - The Kinki District Slide Rule Education Association is formed by a large number of teachers directly involved in teaching.
1956 - The sales department is moved to Konnocho in Tokyo's Shibuya Ward, and capital is increased to 75 million yen.
May, 1956 - O. M. De Leon, the president of Hemmi's representative (De Leon Import & Export Co., Manila) in the Phillipines, visits Japan for the third time.
July, 1956 - A. Richardson (Mr. K. M. (Aub) Richardson), sales manager of Hemmi's Australian representative, E. Esdaile & Sons Pty Ltd., Sydney, visits Japan to discuss the Australian market.
1957 - Seiichi Matsunaga, director and head of sales, visits the US and Canada on a fact-finding mission.
1957 - With the backing of the Ministry of Education and the Japan Association for Mathematics Education, the second open paper contest, inviting papers from teachers on the theme of their methods of teaching how to establish the decimal point position.
1957 - The Kyushu Area Slide Rule Education Association is established, followed by founding of the Tokyo Slide Rule Education Association and the Shikoku Slide Rule Education Association. All of these organizations issued a publication called Slide Rule Education.
January, 1958 - The First Japanese Slide Rule Skill Certification Examination is held, with the backing of the Japan Chamber of Commerce and Hemmi Slide Rule, this resulting in a sharp increase in public awareness of the slide rule.
March,1958 - C. H. Rayner, president of Berrick Brothers Ltd., London, the English representative of Hemmi visits Japan to discuss advertising and the prospects for the future.
July, 1958 - Mrs. E A. Esdaile of Hemmi's Australian representative, E. Esdaile & Sons Pty Ltd., Sydney, visits Japan for talks about expanding the business in that market.
October. 1958 - Hemmi introduces the newly designed Model 2664S 10-inch slide rule, targeted for use in slide rule competitions and certification examinations. This slide rule uses a light green scale, a first in Japanese slide rules.
January, 1959 - The Model P23 (7-inch) slide rule, a new style of slide rule for student use, is introduced, using plastic as a material for the first time.
January, 1959 - 18th issue of the weekly Yomiuri Shukan recommends bamboo slide rules made by Hemmi, classed as a top Japanese manufacturer, in a two-page article which describes the Shirako Factory.

These are easily dated, at least for certain periods, because of family situations. Pre 1935 - Lawrence Slide Rule Company - George Lee Lawrence makes Photographic Slide rules in Chicago. 1935 - Lawrence Engineering Services was set up in Wabash, Indiana 1938 - Moved to nearby Peru, Indiana (10 man shop run by Ed Snyder) c1940 - A glass magnifier was developed c1942 - OEM supplier to Post (model 1446D) during WWII, when Japanese importation was halted. c1943 - Injection molded plastic cursor replaces fragile glass magnifier 1947 - A divorce settlement gives company to wife Vivian, briefly called Lawrence Engineering Company c1948 - Vivian marries Frank C. Bozarth, forms Engineering Instruments, Inc. in Peru, Indiana c1960 - Engineering Services OEM's the 77A plastic American Log Log (Acu-math 1500) 1967 - Company building burns down, Engineering Instruments ceases to exist.

Pickett All-Metal Slide Rules 1943 - Pickett company founded, in Chicago, by Roswell Colvert Pickett, a printer. 1943 - Arthur F. Eckel joins Ross Pickett to form Pickett & Eckel. 1944 - First Pickett & Eckel slide rules made from printed paper card stock are sold. 1946 - The first magnesium slide rules are made, called the Deci-point. 1946 - Ross moves to Alhambra, California to start another division. Chicago company managed by Mr. Florian. 1948-49 - Art Eckel leaves company. Later forms Precision Scale Company. Ross's son, John Pickett, receives BS in Engineering from the University of Redlands 1949-50 - John Pickett receives MS in business from University of Southern California 1949-50 - The Eckel name is dropped from the slide rules and manuals, now just just Pickett, Inc. (purportedly because of a law suit with K&E over using P&E). Corporate name is still Pickett & Eckel, Inc. 1951 - John Pickett joins Pickett Marketing Department Early 1950's - Pickett contracts with Cal-Pan Co. to make aluminum slide rules in Alhambra, CA. 1953-54 - Cal-Pan bought out by Pickett & Eckel. 1953-54 - John Pickett forms Pacific Leather Works to make slide rule cases. 1957 - John Pickett becomes president of Pickett & Eckel, addresses manufacturability issues. 1957 - Pickett abandons machining processes and moves to die cast components 1958 - Pickett cursor production on All-Metal slide rules switches to injection molded plastic parts 1959 - Pickett develops low-cost injection molded all plastic slide rules (100 series). 1964 - Pickett moves to Santa Barbara, CA 93102 USA. 1964 - Pickett family sells company to Times Mirror Co for $1.5 million. Name changes to Pickett Industries.  1964 - Logo becomes a block-font "Pickett" with a small triangle dotting the "i". 1965 - Ross Pickett dies. 1967 - John Pickett leaves Pickett Industries. 1974 - Pickett Industries moves to Nogales, Mexico. 1975 - Pickett Industries combined into Chartpack/Pickett under Chartpack management. 1975-79 - Slide rule manufacturing ends. Drafting supplies continue. 1979 - Pickett moves to Tucson from Nogales. c1980 - Dick Schwartzer buys the entire Pickett slide rule inventory that was destined for scrap 1985 - Pickett Industries sold to Chartpack. 1998 - Manufacturing combined with Chartpack in Leeds, Massachusetts. 1999 - Pickett-Chartpak Industries Division continues manufacturing art and drawing templates. 2005 - Current address: Chartpak, Inc - One River Road - Leeds, Ma 01053 (413)584-5446 2005 - Dick Schwartzer dies. A large inventory of plastic Picketts left unsold. Timeline researched by Bruce Reichelt, expanded by M. Konshak

From 1945 to 1975 the Pickett design evolved to improve quality and to increase productivity. The stock, slide, cursor and logo all are clues to determining the manufacturing dates. Pickett Chronology - Med 183KB Large 1.06MB Large 1.05MB

The following explanations are courtesy of Greg Scott adapted from Greg's Slide Rules Post WWII Aristo rules all have a manufacturing code on one edge of the rule. This is usually a combination of alpha and numeric codes which defines the rule's factory of manufacture, year of manufacture and batch number. Code Details There are three code segments, The factory, year of manufacture and lot number. The lot number is self-explanatory. Examples of date codes: 2FX16 - Manufactured 1969 in lot 16 in Hamburg 4FE02 - Manufactured 1968 in lot 02 in Wörgl 3LS06 - Manufactured 1973 in lot 06 in Geretsried WLS32 - Manufactured 1973 in lot 32 in Wörgl

Factory codes: 1st character, either alpha or numeric. Letter Code Number Code Factory H 2 Hamburg G 3 Geretsried W 4 Wörgl Year Code: 2nd & 3rd Character Up to about 1959 dates were included in the manufacturing code as a number after that the alpha codes were used. A R I S T O F L E X 0 1 2 3 4 5 6 7 8 9 Lot Number: 4th & 5th Character

1761 - The cabinet-maker Kaspar Faber produces his first "lead pencils". 1784-1839 - Anton Wilhelm Faber (1784-1810) and son Georg Leonard Faber (1810-1839) expand the pencil workshop in Stein near Nuremberg, Germany. The company is now called A.W.Faber. 1840 on - Lothar Faber (son of Georg, the fourth generation) produces the hexagonal-section pencil, develops the first quality pencil in Germany and marks it "A.W.Faber" - the brand name is born. 1861 - Lothar von Faber establishes a factory to build slates, drafting equipment and rulers in Geroldsgrun, Germany 1874 - With his petition to the German Federal Diet "for legislation to protect trade marks", Lothar von Faber paves the way for the German Trademarks Act (May 1875). 1880-1891 - Lothar von Faber is made a baron by King Ludwig II (1881) and a hereditary privy councilor by Prince Regent Luipold (1891). 1882 - First Faber slide rules appear made of Boxwood. 1887 - Registered Design D.R.G.M. of 98350 1887 - Adds celluloid facings to Boxwood body and slides 1889 - Introduces framed cursor with glass glued in frame 1890 - A.W.Faber now has 1000 employees 1898 - The marriage of Lothar von Faber's grand-daughter Ottilie to Count Alexander zu Castell-Rudenhausen brings a change of name for the family and the company: Faber-Castell. c1900 - Charles N. Pickworth writes the English versions of A.W. Faber's slide rule manuals. Distribution in United States begins in Newark, New Jersey. 1905 - Firm's name officially changed from A.W. Faber to A.W.Faber-Castell. Trademark still has a stylized balance scale marked A.W.Faber 1907 - Springy-stocks are introduced (DRP 206428) to keep tension on the slide. 1912 - Model number series "3XX" assigned to slide rules. 1912 - Body and Slide now made of celluloid faced boxwood. c1913 - trademark becomes A.W. Faber followed by two framed towers which lay horizontal and bracket the word CASTELL. c1920 - Single-digit Date Codes appear on SR's using the last digit of the year. 1927 was stamped 7. 1924 - Body and Slide now made of celluloid faced Mahogany. 1928 - After the death of count Alexander, his son Roland Castell takes over the chairmanship at age 23. 1930 - A.W.Faber appears only on simple slide rules for beginners. 1930 - Two-digit Date Codes appear on SR's using the last two digits of the year. 1937 was stamped 37. 1935 - Prof. Wather's System Darmstadt slide rule introduced. 1935 - Model number system changes to 1/XX or 1/XX/3XX. Example: "387" becomes 1/87/387 then just 1/87. 4/XX used for 50cm slide rules. 61/ (all celluloid) and 63/ (wood with celluloid scales) used for 12.5cm pocket slide rules. 1937 - Carl Kubler's Brass fabricated Addiator attached to back of slide rules. DRP 655353 pre-WWII - Swiss Pearwood becomes the wood of choice 1946 - Geroldsgrun factory survives war, began slide rule production. 1946-1948 - Beech is used for stocks and slides. Pocket slide rules made of Celluloid. post-WWII - Shortages cause Addiators to be made of sheet metal instead of brass. 1948-1950 - Maple is tried. 1950 - CASTELL appears on left end of the slide. 1950 - 'Special Wood', a composite wood with laminated scale surfaces. 1951 - Production of slide rules from Astrolon sheet resumed. Slides and stocks milled to make grooves and flanges. 1952 - First all-plastic injection molded (Geroplast/Polystrol) closed body slide rules are introduced. 1952 - Injection molded models of previous wood types now add "11" to designator. 1/87 becomes 111/87. 1952 - Injection molded models with new scales systems on closed body SR's introduced, models 57/82, 57/22, 57/88, 57/89, etc. and injection molded Duplex models 52/80, 52/82, etc. 1954-55 - Injection molded Addiator tried, then switched back to sheet metal. 1956 - Castell-Duplex 25cm 2/82, 2/83, etc and 12.5cm 62/82, 62/83, etc appears with screwed on sheet metal end braces. 1962 - Castell-Novo-Duplex 25cm 2/82N and 2/83N appears with screwed on die-cast metal end braces. The 12.5cm 62/82 and 62/83 pocket versions use injection molded braces on one side only. 1972 - Combination Electronic calculator and slide rule designed, Model TR1, TR2, TR3. 1976 - All production of slide rule and calculators ceases. 1985 - Bavaria Film shoots the four-part TV series "Fathers and Sons" in the Faber-Castell Castle, Starring Burt Lancaster, Julie Christie and various German actors. 1991-1997 - Ex-product manager, Dieter von Jezierski, captures the history of Faber-Castell in his book Slide Rules - A Journey Through Three Centuries (Astragal Press).

A.W. Faber Date Of Manufacture Medium 312KB A.W. Faber Date Of Manufacture Large 1.3MB

1915 - Company founded by Claire A. Gilson in his home Niles, Michigan.
c1915 - First Midget circular slide rule, C, L and trig function scales on printed paper glued on 3-3/8" diameter 1/4" thick plywood disk. 2 steel "crow's foot" cursors. Scales have embellishment e-lines.
c1915 - Applies for patent, disk states Patent Pending.
1917 - Son, Richard A. Gilson, is born.
1916-1918 - Slide rule has paper scales glued to 3-5/16" diameter steel disk. 2 cursors on front.
c1919 - Gilson buys Richardson Rule Works from George W. Richardson, presumably for printing process.
1919 - Copyright 1919, Midget type II, printed black scales on white celluloid enamel on steel disk. 2 celluloid cursors, 9 scales. C, CI, L, A, Binary, One turn Log-Log, Fraction, Drill and Thread, Trig functions, CFD.
1-17-1922 - Patent 1,404,019 granted, seven claims, most involve the cursor.
1922 - Midget Type III, printed black scales on white celluloid enamel on 3-3/16" aluminum disk. celluloid cursors on front, 9 scales. C, CI, L, A, Binary, 2 turn Log-Log, Fraction, Drill and Thread, Trig functions, CFD. E-lines removed on front. c1922 - Atlas rule introduced, a long spiral scale on a 10" square substrate.
1927 - Gilson moves family and business to Stuart, Florida. Type III Slide rule artwork reflects new location.
1931 - Copyright 1919 and 1931, Midget Type IV, marked Tavella Sales Co., adds cursor to back. 4-1/16" diameter aluminum disk. All e-lines removed. New trig scales.
c1932 - Midget Type IV, Version II. 4" diameter disk. Printing has no reference to Gilson, presumably because of OEM sales to Dietzgen, Post, and others.
c1932 - 8" diameter version of midget, called "Apex" is introduced. (this will be rename "Binary" later.
1934 - Commercial calculator, 4-15/16" diameter disk, white celluloid enameled. Scales C, CI, Rate, Day, Month, Year.
c1935 - Midget Type V, No e-lines or Log-Log, more detail on C scale. Shows Copyright 1931 and patent date 1-17-22. 4-1/16" diameter disk.
c1935 - Atlas rule changed to 8-5/8" diameter disk. Richard Gilson, still a teenager, calculates and draws the scales and divisions, resulting in a 75 foot effective scale good for 4 decimal places.
1936 - Copyright 1931 and 1936, Midget Type VI, light cream color, 4-1/4" diameter disk. Key marks on C scale extended. Artwork shows just "Patented". (patent may have expired).
c1936 - Apex renamed to "Binary".
c1939 - Midget Type VI, version II. Plastic celluloid 4-1/4" diameter disk, 3 cursors. Shows copyright 1931 and 1936. No mention of patent.
c1945 - Midget Type VI, version III. Green celluloid on aluminum. Shows "Patented", Copyright 1931 and 1936. OEM to Post 44EAE630, Dietzgen 1797M. Manuals show Gilson Slide Rule Company, Stuart, Fla.
1960 - Gilson Slide Rule Company sold to Daniel W. Fagen, a local machinist and owner of a moving and storage business. Business remains in Stuart, Florida.
c1960 - Clair Gilson dies before being able to fully train the new owner in the production techniques. Fagan studies the stamping presses, plating, printing and polishing equipment and continues production as a family operation.
1968 - Leatherette pouches are now heat seamed, instead of stitched around edges.
1968 - 1968 Dieterich-Post catalog shows Midget 4" diameter. (no. 2555) and Binary 8-3/16" diameter. (No. 2560) in catalog. States white celluloid over aluminum disks.
c1970 - Gilson Binary Slide rules are listed in a Teledyne-Post Catalog. (Teledyne bought Post in 1968).
c1975 - Daniel Fagan sells company. Aside from the new owner's lack of mathematical ability and inexperience with machinery, Gilson's demise was associated with the same fate as other manufacturers with the arrival of the electronic calculator.

Thanks to Peggy A. Kidwell, Curator of Mathematics,Smithsonian Institution for contributing research. Smithsonian museum's trade literature, the Proquest newspaper database, and the Social Security Death Index.

Provided by Daniel Toussaint, France

Copyright © 2003-2006 International Slide Rule Museum