Line scales are important physical standards of length used for accurate positioning or measurement in one, two or three dimensions. Depending on the application, line scales can have dimensions from fractions of a millimeter to several tens of meters. For example, small scales are used to calibrate the field of view of optical microscopes. Scales with dimensions in the meter range are used to read out the position of machine tools and measuring machines, while leveling rods find their use in geodetic surveying. Accurate calibration of scales requires dedicated equipment and measurement conditions that are usually only implemented at the national metrology institutes.