Slide rule workshop I

Chris' mystery slide rules Nr. 3

Two slide rules with special figure

Click images for magnification

Data:

  • 2 nonames with same special figure
  • Timber with plastic scale
  • No text at back side

Questions:

  1. What does the special figure mean?
    This “special figure” commonly appears on early Hemmi rules. Hemmi expert Paul Ross describes them in JOS Vol. 12, No. 1, Spring 2003, pg 41 as “Mnemonic Indicators” that were phased out in the 1930s. David Rance
    See Decimal point Leo van der Lucht
     Was used as a symbol for calculation corrections in multiplication or division: (+ = comma to the left, − = comma to the right) Jean Paul Hild
  2. Name?