A unit of angular velocity equal to 15o per hour (one revolution per day), the rate at which the earth rotates on its axis. This unit is used to measure the drift rates of gyroscopes and various pointing devices in aerospace engineering
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}