Under this banner, we include different facets of slide rule theory. One of the biggest problems facing beginners is the placement of the decimal point. The slide rule does not do this (although some special types of slide rules do). Hence it is important to master, or at least become proficient in one or more methods of estimation/approximation.

Estimation techniques are important regardless of what type of user or what you do. One of the most common and probably easiest forms of estimation is using scientific notation, so some treatment is given here.

The Pickworth Modified Digit Counting Method is also included here for interest, and use. Out of the digit counting methods, this is one of the easiest to use.