You simply hit the MARK key, on the G-III, etrex, 76, and emap press and hold the ENTER key, and the waypoint entry form will appear.
You may find other uses as well such as when your hat blows off you head driving down the road.
If you want to save that location then you should rename it since it will be overridden by the next MOB sequence.
These names are three digit numbers starting with 001 and incrementing each time you create a new waypoint.
Even if you rename a waypoint the unit will generally assign the next number in the sequence anyway and will not reuse the numbers until it reaches 999.
These database waypoints are discussed in the chapter on databases. On most unit they must be no more than 6 characters long and contain no spaces but can contain any combination of letters and numbers and some punctuation.
The newest units permits 10 character names and these can include spaces.This will store a special waypoint at your current location named MOB and will automatically start the navigation features of the unit to aid you in navigating back to that point.A position marked in this way is designed as a safety feature for boat use when someone might actually fall overboard.On the G-III family and emap you first save the waypoint and then you can average by selecting this option from the local menu on the waypoint display screen.(Please see more information on averaging below.) If you are using dgps you can still average the position but the improvement will be much less since dgps is already more accurate.Satellites close to the horizon will have good satellite geometry when coupled to one high unit but they suffer from atmospheric effects which can make the accuracy worse.