PEC

Abbreviation: Periodic Error Correction – Most astronomical mounts use mechanical gears/worms driven by electric motors. Regardless of cost, no gear/worm can be made perfect. Due to manufacturing tolerances, material or engineering skill each tooth on a gear cannot be made identical. This results in the mount, at times, running very slightly faster or slower than desired. Since the set of gears is mechanical, the physical relationships between the gears that result in the errors occur in the same position during each full cycle of rotation. This defines periodic error. This error can be characterized by analysis of the mount’s performance. Using this analysis, the electrical motor then can be run slightly faster or slower at the appropriate times to compensate for the mechanical error.