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## Hemmi Slide Rule Catalogue Raisonne

## **Scales on Hemmi
Stadia Rules**

We have modernized
the scale names on stadia slide rules but the M_{1} and M_{2}
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).
- C
_{1}: Logarithmic
1-10. Duplicate of D scale on lower stator. We have called
this scale "D."
- M
_{1}: Set Q (in the range 5^{o}46'
to 45^{o}) on the leftmost 2/3 of this scale; read the value of
SinQCosQ on the C_{2}
= C scale. Set Q (in the range 45^{o} to 0^{o})
on the rightmost 1/3 of this scale; read the value of Cos^{2}Q from the C_{2}
= C scale.
- M
_{2}: Set Q (in the range 35'40"
to 5^{o}46') on this scale; read the value of SinQCosQ on the C_{2}
= C scale.
- C
_{2}: 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.