This equipment was originally designed as a pilot aid to facilitate the use of maps on a route flight. It was used to such an extent that several different models have been developed which fall into the category of automatic navigation equipment. However, even the new concept is still an open-loop navigation device, the loop being closed through the pilot or navigator in the aircraft who reduces the accumulated position errors to zero by direct observations. In the most sophisticated form the roller map equipment is driven automatically according to aircraft ground-speed derived from doppler instrumentation and is equipped with an aural flight programme replay device to draw the pilot's attention to salient features of his flight route.