In the world of encoders, the terms resolution, accuracy and repeatability are often confused, and sometimes even thought to be synonyms. Before we can talk sensibly to each other, we need a common language, so we’ll start with some definitions. This article refers to rotary encoders because they’re much more common than linear, but the interested reader can easily extend this discussion to linear encoders as well.

Resolution is a measure of how many counts per unit distance the encoder generates, or, inversely, the size of the measuring step. With rotary encoders, resolution is expressed in either units of angle (degrees-minutes-seconds, decimal degrees, grads, or radians) or in number of measuring steps per revolution (e.g., 10,000 counts/rev). [PPR, or pulses per rev, is quite common, but we avoid this term on purpose.] Often, when a binary number of measuring steps per revolution is required, the term "bit" is used to indicate the resolution’s highest power of 2; for example, a 16-bit encoder generates 2