Novatel MERLIN EX720 User Manual page 54

measurements of signals from nearby cellular base stations
(towers) and reports the time/distance readings back to the
network, which are then used to triangulate an approximate
location of the card. In general, at least three surrounding
base stations are required to get an optimal position fix.
Note: AFLT accuracy is limited by the geometry of the cell towers
surrounding the card requesting location information.
If you are outside you may be able to obtain an updated GPS
fix more often than once an hour depending on the level of
visibility.
Weather conditions may also limit your ability to acquire a
GPS fix while outside.
48 Section 2C: Menu Options