There are a few instances in which you may want to perform a master reset on your Foretrex 301 or 401, such as:
All settings, user data*, and satellite data may be erased when resetting the GPS. User data can be backed up to the computer, therefore refer to the FAQ article "How do I back up user data from my outdoor GPS with a USB interface?" before performing the reset.
To perform the master reset:
The device will now reboot and is reset. You will want to leave the device outside with a clear view of the sky for a minimum of 20 minutes to acquire satellite data.
*User data consists of waypoints, routes, tracks, and geocaches