1. This is the only simplex rule for which I show both front and back views. The reason for this is the summary instructions on the back of the rule. I show below examples for multiplication, division and scale reading. In addition to these detailed views the back also covers: definitions, logarithms, sine and tangent scales, and calculation of square and cubes. It also has a table of decimal equivalent of fractions - in 64 ths. This gives rise to the question "Were slide rule books really necessary?"