## Scales on Hemmi Stadia Rules

We have modernized the scale names on stadia slide rules but the M1 and M2 scales remain mysterious to non-surveyors.  Here is a description of the front scales on Hemmi stadia rules, models 90 - 96.  Note that there are two calculating scales on the bottom edge of the rule. • L:    Standard linear scale for determining common logarithms.  Value on this scale = Log(value on D scale).
• C1:  Logarithmic 1-10.  Duplicate of D scale on lower stator.  We have called this scale "D."
• M1:  Set Q (in the range 5o46' to 45o) on the leftmost 2/3 of this scale; read the value of SinQCosQ on the C2 = C scale.  Set Q (in the range 45o to 0o) on the rightmost 1/3 of this scale; read the value of Cos2Q from the C2 = C scale.
• M2:  Set Q (in the range 35'40" to 5o46') on this scale; read the value of SinQCosQ on the C2 = C scale.
• C2:   Logarithmic 1-10.  Like D but on movable slide.  Just "C" in modern nomenclature.
• D:    Logarithmic 1-10.
• A:    Logarithmic 1-100.  Value on this scale = (value on D scale)2.
• K:    (Bottom edge of rule, read from a pointer aligned with center hairline.)  Logarithmic 1-1000.  Value on this scale = (value on D scale)3.
• IA:   (Bottom edge of rule; read from offset pointer.)  Logarithmic 100-1.  Modern notation would call this scale "A inverted" or "AI."  Value on this scale = 1 / (value on D scale)2. Pointer offset varies from model to model; on model 90 (10") the corresponding value on the D scale is read from the rightmost hairline; on model 96 (20") it is read from the center hairline.