The Holox BT541 uses the Skytraq Venus 521 chipset which supports AGPS. Skytraq provide a free AGPS download application for Symbian and Windows. Time to lock, and typical accuracy are very good when AGPS is used (can be a bit tempramental without it). Early firmware versions had problems with track drift (firmware is upgradeable, but difficult to find the latest version). The BT541 has a motion detector (sounds like a ball bearing in a box) that allows the device to go into a low power mode when not moving. This can give a battery life of many days depending on usage.