There are some obstacles that can affect the GPS accuracy. 1. After a period of disuse, GPS signal may be delayed during reactivation. - More than 3 days : Operates in a cold-start state due to GPS receiver battery discharge. Up to 30 minutes may be required for normal operation. - More than 1 day : GPS receiver operates in a warm-start state. Up to 5 minutes may be required for normal operation. - 2 to 3 hours : GPS receiver operates in a hot-start state. Up to 1 minute may be required for normal operation. 2. GPS signal may be delayed if device is located within a GPS dead zone for an extended period. Even when power is supplied, the GPS receiver may experience a loss of signal and out-of-route warning or disconnect. 3. GPS signal rate may be degraded by interference from vehicle windshields having metallic tinting, radios, MP3/CD players, GPS camera guides and other electronic devices. 4. GPS signal rate may be degraded by tall buildings, overpasses, and when passing through underground roads or tunnels, resulting in signal interruption, out-of-route warnings, or disconnections. 5. Some atmospheric conditions like rain or snow can weaken the GPS signal. Heavy clouds, thick fogs or snow could be a hindrance for the signals to reach GPS receiver.