There are 49 different types of common slide rule scales. These scales are labeled with a letter and sometimes a sub-letter or number when integral functions of the letter are broken down into smaller components. The main labels are A and B, which measure scale of squares, C and D which examine fundamental slide rule calculations and K, which measures scale of cubes. Other scales that are seen often include L, which is log scale, S for sine and cosine measurements and T for tangents and cotangents.
All duplex models have scales on both sides of the main body and the auxiliary sliding unit. The measuring unit is built so that the measurement on one side relates directly to the measurement on the other. Users of this type of scale must exercise caution in manipulation between sides to decrease reading errors. These models feature uncommon scales such as LL01, LL3, R1, R2, Sq1 and Sq2 in addition to many others. Versions from different companies will provide different scale arrangements that may be more useful to some consumers than others.
Circular slide rules have an increased capacity for scale length due to the unique design. These models can have a single round disk capable of movement in addition to a second rotating disk. These rules tend to be the least popular as they are subject to the highest level of manipulation errors when transferring between the scales. This type of slide is commonly used by pilots and can be used in conjunction with basic flat slide rules in duplex or simplex designs.
Simplex or desktop slides include the Mannheim, Rietz and Darmstadt models. The Mannheim features A, B, C, D, K, S, L and T scales. The Rietz scale is similar to the Mannheim but the scales are located in different areas. The Darmstadt scale is for log and Pythagorean scales and includes K, A, D, P, S, T and L scales. This scale comes in two different arrangements as the initial design required the movement of the slide to an unusual position, which confused many users.