1. This slide rule was used engineering calculations. On one face there was a "Routledge" type engineer's rule and on the other face a special slide rule for calculating the weights of steel.
2. The rule is folded at 188 since 1 ft of steel with a with a cross section of 188 mm2 weighs 0.1 lb. (304.8 mm * 188 mm2 * 17309 lb / m3 / 1E6 mm3/m3.)
3. The calculation is done by setting the width in (mm or 1/8") on the C scale against the thickness (in mm or 1/8") on the D scale. Against the length in feet on a A scale read the weight in pounds on the B scale. This works for 1/8" and mm since 1/8" is 3.175 mm and 3.175 squared is 10.08. If the values are entered in 1/8" the result is of course 10 times higher than if entered in mm.
4. The rule also has tables for weights of materials and power of steam engines.
Detail - back right - showing scale folded at 1.88 and tables.
