An object tracking system includes a plurality of tags. Each tag includes
a mechanism for transmitting a triangulation signal and a position signal
that is indicative of a change of position of the respective tag in a
time period since a respective reset event. A plurality of triangulation
stations receive the triangulation signals from the tags. At least one
antenna receives the position signals from the tags. A computer is
coupled to the triangulation stations and to the antenna. The computer is
programmed to switch between (a) a first tag location algorithm to
determine a current location of one of the tags using a differential time
of arrival procedure based on the triangulation signal, and (b) a second
tag location algorithm to determine a current location of the tag based
on the position signal transmitted by the tag and a previous known
location of the tag.