International Workshop AV

Mike's unknown Hemmi slide rule.

20-inch

Click image for magnification

Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation Hemmi Triangulation

Data:

  • 20-inch Hemmi
  • Off-centered rear window.
    The narrow slots are part of the construction, not for calculation.
  • Special scale arrangement
    Front: 50cm / e = L N½ N⅓ T N = X ] 20inch
    Back:  = S logS α =
  • The characters on the sleeve translate as “Type 97 slide rule” according to Google Lens.

Questions:

  1. Does this have a proper name or model number?
  2. What was its purpose; perhaps military, aerial photography?
    This is listed on Paul Ross’ Hemmi Raisonné “second page” – i.e. Hemmi’s with no model number. A lot is uncertain but he catalogues it as “Triangulation Rule, ca 1940” – “… Altitude Correction/Height Adjustment Rule above but his friend Atsushi Tomozawa suspects it was used by airplane navigators or for aerial surveying.” David Rance