Just to give you a hint about how they work, slide rules are based on the geometric mean rather than the arithmetic one: halfway between A and B on a normal ruler you will find ½(A + B), on a logarithmic scale you will find √(A × B).
Due to exponent rules this makes it possible to use two logarithmic scales to compute A × B / C in the following way:
1. Line up one scale’s A with the second scale’s C.
2. Look for the second scale’s B on the first scale.
When you're multiplying, C is usually 1 or 10 (this would usually be done with scales labeled C and D) and when you're dividing B is usually 1 or 10, but sometimes your problem works out that you can just do both at once.
Due to exponent rules this makes it possible to use two logarithmic scales to compute A × B / C in the following way:
1. Line up one scale’s A with the second scale’s C.
2. Look for the second scale’s B on the first scale.
When you're multiplying, C is usually 1 or 10 (this would usually be done with scales labeled C and D) and when you're dividing B is usually 1 or 10, but sometimes your problem works out that you can just do both at once.