DESC: This dual axis motor drive, with drive corrector capabilities, is designed for Celestrons CG-4 mount. It precisely controls the telescopes tracking speed during long, timed exposures of celestial objects, producing the best possible image sharpness. Precision drive correctors are a must for those with a serious interest in astrophotography or CCD imaging. Four speeds are available-1x (sidereal), 2x for guiding, 4x, and 8x for centering.