No matter how well designed or carefully bled a hydraulic steering system is, there will always be some amount of air trapped in the line. As the autopilot works, the air can be compressed to the point where the air bubble bursts, causing the autopilot to compensate for the change in pressure. Though the corrections are small, they can compound over time, causing the autopilot to work overtime and the course to zig-zag slightly. Though the Evolution line of autopilots is designed to adapt to a boat’s steering characteristics, until the development of Hydro-Balance, they couldn’t account for the air. Engineers, though, developed software that can. The result: a wakeline that’s true as an arrow and probably more important to sailors, less power consumption by the autopilot.