GLONASS (Global Navigation Satellite System) is an alternative positioning system to GPS. With GLONASS enabled, your watch may record a more accurate track in certain conditions. Particularly in urban areas with tall buildings, GLONASS can improve track accuracy. In other areas, it is typically best to leave GLONASS disabled. With GLONASS enabled, your watch consumes more battery life.
To toggle GLONASS on/off:
The GLONASS setting is a global setting. When you enable it, GLONASS is activated for all sport modes with GPS.