Rock City Marine Wikipedia
Rock City Marine is a manufacturer of marine electronics, specifically for sailboat racing, based in Detroit, Michigan. Founded in 2007, Rock City Marine develops and manufactures the RockBox A.M.P.D., Advanced Mobile Performance Device, a GPS based instrument tailored for the racing sailor. Metrics used to increase the performance of a racing yacht, such as speed, course, and VMG, are calculated based on GPS position data and displayed in numeric or graph form on a graphic LCD. Unlike traditional marine instrument systems, the RockBox is self-contained and requires no wiring to external sensors or power sources.