Otis King Calculator [Spiral Slide Rule] Mid 20thC

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A very nice working example of the Otis King Calculator or spiral slide. Comes in its original box with retailer A Johnson, Tottenham Court Road, London.

Otis Crater Formy King [1876-1944] patented this spiral slide rule in the early 1900’s. In 1922 Carbic Ltd of London began to manufacture the instrument and continued to do so until 1970 when it became overtaken by modern day digital calculators.

The patent is really in our view stolen from the larger spiral slide rule invented by Fuller. Nevertheless, the handy nature of the Otis design made the instrument fairly popular.

This is a very good example of model K [there was a model L and that’s all] with two scales 414 at the bottom and 423 at the top. The original instructions are present although it doesn’t take Einstein to work out how to use it – part of the appeal.

There is a raft of information online including average youtube videos on how to use it … get the right one before you are put off. The guy who invented the computer mouse started a fanatics website which is fantastic and is building a database of information regarding existing instruments ... even down to whether the instructions are stappled!

The retailer was founded by William Johnson [1837-1900] an optical and scientific instrument maker always at Tottenham Court Road - he had passed away before King got going with his calculator - the sons of Johnson continued in their fathers footsteps.

Collectable mathematical calculator by Otis King

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