In the past, general aviation autopilots have only flown flight paths by either tracking or coupling to Course Deviation Indicator (CDI) or HSI needle deflections. Due to deflection variations and noisy signals, the system might experience wandering. Tracking is simply the system reacting to signal input often providing very rigid flight turns and maneuvers for the autopilot. Roll steering commands are based on known location, flight path, speed, and anticipated turns & maneuvers. Therefore, autopilots enabled with GPS roll steering can fly the aircraft more precisely and smoothly.