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Mysterious circular slide rule
Information wanted about this cicrular slide rule.
Brand name: Dumont. French origine, hand made, built around 1860. The disc consists of five metal discs with handles to make independent rotational movement easy. Rings 2 and 4 are fixed. Rings 1 and 2 have scales ranging from 0 to 24; rings 3, 4 and 5 from 0 to 60 which suggests the application of time calculations. There is no logarithmic scale.
The slide rule is pretty heavy: a few kilogrammes.
At the back side there is a number: 1835 which is not a year. Due to the owner it is a 'faked' serial number to give the false impression that lots of these slide rules were made and sold.
If you have any information, ideas, suggestions or speculations about this rare collector's item, please fill out the email message which you'll find under CONTACT to the left.
The owner will be most grateful. | 
