You can test how good your puck location is by using the satellite detection on the main menu - press the map button when on Nav page and go through the menu until you see GPS and look at how you doing for satellite detection,it will give a value.
5 plus satellites is required for it to perform to a decent standard.
Or as someone else wrote
Press the map button twice to display the split screen (if it's not already shown), then in the drop down list on the split screen, select GPS Viewer. That will tell you how many satellites the unit is currenty tracking.