Slide rule workshop S

Fred Astren's mystery slide rule

A German Soho?

Click images for magnification

The front of the slide rule
A detail with the only identifying marks
A detail of the indicators for reading the reverse of the slide
SINUS, TANGENT, LOGAR

Data:

  • Early Soho configuration made of boxwood
  • Brass chisel-edge cursor
  • 25-cm scales
  • The body length is 27 cm.
  • Reverse of the slide is marked: “SINUS”, “TANGENT”, and “LOGAR”.
  • Purchased it on eBay Germany in 2016 from a seller who lives in a village in Bayern.
  • Note: Soho ist an early type of standardised sliderules which James Watt produced in a factory in Soho, it has normally 4 scales ABCD, C ist doubled to calculate roots with D which ist from 1 to 10. Normally it had no cursor. (Wolfgang Bode)

Questions:

  1. What is this?
    The markings on the L scale are a bit unusual. They are the same as those on this Tavernier-Gravet slide rule. Eamonn Gormley
     I think they are the usual markings of Tavernier-Gravet Soho slide rules. I have some examples in my collection with the same markings. Marc Thomas
  2. Why are there dots in each division between 1 and 2 of the two upper scales?
  3. There also appear dots in some divisions of the C scale. Are they intentional?