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The Fraction Of an Inch Adding Machine / Fractron

Description
Video
Simulation
History
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Patents
Links

The Fraction Of an Inch Adding Machine, or Fractron, is simple disc adder. It consists of three discs made of aluminium. The front and the back disc are riveted together. This sandwiches the middle disc though it is still able to rotate because it is really a ring rather than a disc. The moving disc has 64 holes evenly spaced about its rim, representing the fractions of an inch from 0 to 63/64. The stationary front disc shows these fractions in lowest terms and in a decimal representation. Using a stylus you can dial in any number of these fractions, and the total amount is displayed through a small window in the front disc. To reset the display to zero use the stylus on the hole that is marked in black.

The machine does not have a carry mechanism, but there is a notch in the outer disc and a tab on the moving disc. When you hold the disc you can put one finger in the notch. When the addition reaches a whole number of inches, the tab can be felt moving past the notch, alerting you to the fact that the result overflowed.

The machine came with an instruction leaflet.

Video

Below is a video I made that demonstrates the Fraction Of an Inch Adding Machine.

Simulation

You can try out the Fractron in the simulation below, or open this simulation in a separate window.

History

The Fraction Of an Inch Adding Machine was designed by Kurt P. Jaeger. He started making and selling them in 1951, and patented the design in 1952. The first ones he made came in a cardboard box, and the centre of the disk was black and had his name on it.

The most common version is the one I have which came in a plastic sleeve. Its centre is blank with the design patent number in small letters along the bottom. These were ideal for promotional use, so there are many which have a logo or advertising slogan printed in the centre. I don't know when and for how long this version was manufactured, but I assume this was probably from the late 1950s, possibly until the late 1970s. It seems that it was given the more catchy name Fractron during this time. Mine has a sticker on the instruction sheet and one on the back of the machine, both bearing that new name. The address on those stickers is in Fort Lauderdale, very close to Kurt Jaeger's Miami address, and in the metal is stamped "Sheridan Printers, Fort Lauderdale". Note however that others exist with different manufacturer names stamped in the metal, for example Sheradco, Inc. in Detroit.

A certain Anthony Pickios may also have been involved in the manufacture, as in 1969 he was granted a patent for a draftsman kit that included the Fractron in its contents. In 1982 he received a patent for an improved method of manufacturing them, and from then on the centre of the disc included the new patent number and had the name Fractron was written diagonally across it.

Advertisements and Articles

I found almost no advertisements for this machine in online archives, except for a single advert from January 1951, and a Sheradco mention from April 1958.

Patents

Here are the patents relating to the Fractron, including some predecessors.

Links

Rechnerlexikon has a page about the Fractron.
Evil Mad Scientist Laboratories has a page with instructions for making your own.
Chris Staecker's youtube channel has an amusing video.
Wikipedia's page on Adding Machines includes a nice picture.

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