Zenith.

Data:

• This metal circular Slide Chart — it is not a Slide Rule — has the name Zenith and is Swiss made. Switzerland is famous for its watches and there exist even a watch manufacturer with the name Zenith.
• This Slide Chart has on the outer scale numbers up to 24, what could be related to the 24 hours in a day, a scale from 0 to 1440, which might indicate minutes in a day, and an inner scale 0 to 100 %.
• All scales are linear.
• There is no information on the rear side.
• There exist more Slide Charts with the name Zenith. It seems that Zenith is specialised in and producing circular disks for all kinds of purposes, such as radiofrequencies disks, but also part of the top of a hand vane soil tester, disk for a balance, disk for an inclinometer (in The Netherlands sold under the name Plastimo), as medical instrument, etc.

Questions:

1. Is Zenith a manufacturer or a company which sells circular disks for all kinds of purposes?
   More patents by Fabrique des Montres Zenith
2. Does the Zenith disk belong to the Zenith watch company?
   The disk is “A calculating device for the record diagrams of apparatus recording periods of operation of machines or vehicles” described in patent GB 382589 issued to “Fabrique des Montres Zenith” of Le Locle, Switserland, in 1932. Andries de Man
3. What is the purpose of this Slide Chart?
   
   GB 382589 animated
   It adds time intervals that are recorded on circular paper charts. So it is not a slide chart but an adding device! The registration chart is rotatably mounted around the central axle. The addition occurs by manually turning the cursor, if the machine was working, or turning the paper chart in the opposite direction, if the machine was not working. Andries de Man
4. What is the purpose of the % scale?
   The percentage scale is the percentage of a full day. Andries de Man
5. Are other companies known who are specialised in comparable disks for a wide range of purposes?
   One example is Schilderfabrik Hans Meierhofer AG, Mellingen, which is not specialised in disks but did make metal calculating disks for various purposes.
   See also “Leo's unknown black disc” Andries de Man
   Another example: the Green computer Alistair Pearson
   The London Name Plate Company Peter Hopp