Electro-mechanical rotary encoders serve the need to track the shaft movement in industrial and commercial equipment. These devices convert the angular position or motion of the shaft to analogue or digital code. Absolute encoders reveal the position of the shaft, with each position of the shaft providing a different binary output. Incremental or relative encoders, mostly used in industrial settings, reveal the motion of the shaft. Both these types of rotary encoders find use in industrial control applications, robotics, radar platforms, computers, special photographic lenses and other places. Data from these encoders is vital to calculate speed, position and distance, with precision. Rotary encoders are available in magnetic and optical types. When purchasing a rotary encoder, consider counts or positions per turn, the level of accuracy and the speed range. The form factor and ruggedness are also important for installation. Installation may require accessories, such as bellows and couplings. Some equipment, such as transport belts, may require length-measuring systems as well. These systems, consisting of components such as shaft encoder, spring arm and measuring wheel, measure speed and length. Spring encoders measure length in locations with adjustable positions, and may be installed at a long distance from the point of measurement.