What is the biggest source of angular error?

Scale mounting eccentricity error is the biggest source of angular error. For example, on an 18 mm scale, if the scale is mounted 0.1 mm off-center, there will be approximately 0.9 degrees of angular error. The eccentricity calibration of Aura Series product helps to reduce angular error. Eccentricity error will also tighten the alignment tolerances.