The Atlas 50 foot slide rule

Most slide rules are 10-12 inches long and accuracy is difficult. The Gilson Atlas circular slide rule has three scales on its front. One is 23 inches long, the other is a 50 foot spiral [other sources give the length as 75 feet but a page from the instruction manual is reproduced below and gives the length as 50 feet].

Results on the outer 23 inch scale can be read to three figures and  on the central spiral to  five figures.  The innermost scale may be intended for counting rotations around the spiral.

The disk is 8 and 5/16ths inches in diameter and 5/16th inches thick. It is made of aluminium covered in white celluloid enamel. There are two cursors on front and one on the back.

The Atlas slide rule was produced by the Gilson company, founded by Clair Amasa Gilson


Clair Amasa Gilson [1889-1962] was born and raised in Niles, Berrien Co., Michigan. He held a degree in engineering from Michigan State University.

Clair married his wife Clara in Michigan about 1916 and they had two sons; Richard in 1917 and Stuart in 1919.

He was unable to serve during World War I due to having “Brights Disease”.

Clair Gilson was a civil engineer and developed a circular slide rule for use by banks, businesses and accounting offices. This new form of a slide rule was patented by Gilson on October 19, 1915 and was considered far more accurate than the traditional straight slide rule.

The very first circular model was printed paper glued to a 3 5/16” plywood disk. Later it was placed on a 4” steel disk. He began selling the new circular slide rule in Niles, Michigan. The original symbol for the business was the “Be Wise” owl.

About 1919, George W. Richardson who owned Richardson Rule Works (for figuring the scales), sold that business to Clair Gilson. Additional patents by Gilson included a Mechanical Calculating Device in 1922.

By 1927, Gilson with his wife and sons had moved to St. Lucie County, Florida.  The Gilson Slide Rule Company was re-established near Bessey Creek along the North Fork of the St. Lucie River at the southern edge of St. Lucie County.

Gilson slide rules included the Gilson Binary Slide 8, the Midget Slide Rule (with a diameter of 4″) and the Gilson Atlas Slide Rule.

Orders for the slide rules came from all across the United States and many foreign countries. In 1930, a Gilson Slide Rule could be ordered for $2.00.

Gilson made rules for many other manufacturers. These were sold under the brand names Atlas, Midget, Post, Lietz, Dietzgen, Bruning and Travella.

The Gilson family carried on a highly success business over the decades.

By the beginning of the early 1960s, Clair Gilson’s health was in a serious decline. Daniel W. Fagen, a long time friend and businessman in the area had continuously asked Gilson to sell him the slide rule business. Clair finally agreed and the sale was made final in May 1, 1962.

Just a few weeks later, Clair passed away on May 17, 1962, at the age of 72 years old, unable to completely instruct Daniel on the full manufacturing process of the slide rules. A road near Britt Road, close to the Gilson home and slide rule company was named Gilson Road.

Daniel Fagen with his wife Roxine, owned the Fagen Transfer Storage Company on Flagler Ave. in Stuart, FL. Daniel moved the slide rule operations and equipment to Flagler Avenue. By trial and error he learned the process and especially how to construct parts for the manufacturing equipment, much of which was over 40 years old.

By the early 1970s, Fagen sold the slide rule business to another individual, who also had to learn the process. However, he was unable to achieve any success from the business since the new electronic calculators had come onto the general market and were highly successful.


Filed under Calculators, History

11 responses to “The Atlas 50 foot slide rule

  1. DWF

    Another interesting fact about my father, Daniel W. Fagen, is that he never completed high school (but he did complete a GED). He left school to work in Western phosphate mines and worked as a welder for the Navy. So here is a man manufacturing slide rules, without much formal education, and with little training from the inventor.

    He was self-taught in many trades and a very avid reader, however, and a talented machinist. He eventually got a job at Pratt and Whitney aircraft in West Palm Beach until his retirement.

    Daniel W. Fagen II

    • Never was much with slide rules, the stick kind. Had a high end Dietzgen, which I gave to my younger brother, when he studied engineering, he passed it on to his son, when he too studied engineering. I was a Piping Designer/Field Engineer type. For pipe fabrication calculations, developed lengths of offsets, rolled and otherwise, we used Smoley’s Tables. We had to give fabricators dimensions good to 1/16″, no way to get that with any slide rule I ever saw.

      Lately, seem to have been bitten by the Circular Bug, Gilson persuasion. Have acquired a couple via ebay, the things are certainly fascinating, though the 4″ type are harder to read with my old eyes. Anyhow, the non-electric virtue of the slide rule remains, just like with celestial navigation. One can rely on the proverbial “black box”, the GPS Unit, or use a marine sextant, a good time piece, readily available these days and whichever of several different tables one picks, no batteries required with the latter outfit, which works fine for ocean navigation, or shooting position while ogling passing females on the beach..

      All the best.

  2. John M. Foster

    Having moved to Stuart in 1962 and attending high school there my chemistry & physics classes utilized Gilson slide rules. For very discounted prices we could buy their products. I still have my 8″ diameter standard, a 4″ “mini” and the top of the line “Atlas”. The Atlas was the hit of my surveying class at the Georgia Institute of Technology because it could produce 4-5 decimal results while the rest of the class was multiplying the same numbers by hand … Needless to say the entire class purchased an Atlas.

    John M. Foster – Architect
    B. Arch ’77

  3. frank

    do you have any for sale?

    • John Foster

      Unfortunately I only have the ones mentioned in my comment which are not for sale.

      John M. Foster – Architect – AIA

    • Alan

      I would assume, perhaps incorrectly that you are aware of ebay. You might give them a try, Enter circular slide rule in the search field. Good luck.

  4. John M. Foster

    Unfortunately, I have only the ones mentioned above which are not for sale. Gilson Mf’g. also produced a magnetic hurricane chart about 20″ x 30″. When I moved to Stuart in 1962 quite a few businesses had one on display. Haven’t seen one in years …

  5. alan

    I recently acquired one of the above pictured Gilson Slide Rules, an Atlas. No manual came with it, however I have downloaded a brief commentary entitled How to use the Atlas Circular Slide Rule (Spiral Type). Was or is there a more detailed version available? Any information or direction much appreciated. Thanks

    • John M. Foster

      I do not think that I have an instruction manual. In my (fuzzy) memory, it seemed that use of the long scale was the same as the obverse side, don’t know how to determine which section of the spiral to view. I think that you had to be aware of the approximate result and read the numbers ……. Try a few calculations in which you know the result

      John M. Foster – AIA – KB4IE

      • alan

        Sounds like a plan. Will have to test the virtues thereof. Blundering about on The Internet, I did come upon a Slide Rule Manual, for using the Atlas Slide Rule. The thing is under the Dietzgen name,and is a few pages in length. I guess that this is just about all one might find, though I will continue searching. Thanks for your input.

      • John M. Foster

        Again, a long ago memory – The Gilson “manual” was a few horizontal 3″ x 5″ pages with a green 90# cover simply stapled together. This was likely printed & bound by Southeastern printing, located just south of Stuart on Old Dixie Highway. Please e-mail me at – I have a rather large stack of boxes in my utility room, somewhere in these boxes are my 3 Gilson slide rules & (maybe) instruction manuals. If found, I’ll scan & upload …

        Best wishes,

        John M. Foster – Architect – AIA

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