How should a GPS be set for overseas use?

There are three answers to this question

1. In the UK we should always be using OSGB settings....
   Our UK maps are accurate and they are overprinted with grids.


2. When doing surveys for RWH overseas we must always use UTM
   When following RWH tracks overseas we must always use UTM
   Selecting UTM will cause the GPS to select WGS84 as the Datum. Please mark the Coordinate System as UTM.
   (WGS84 is not a Coordinate System: it is a datum giving precise description of the Earth's shape)
    
3. If you need to locate your position on a local map, you will have to use the same Coordinate System settings as (hopefully) marked on the map.

• There is a conflict between 2 and 3 and no easy answer
• If you do not use local settings for 3 then usually the error will vary from zero (common) to 100m+ (rare)
• My own experience suggests that using a GPS to locate yourself on an overseas map is a sometimes overrated pastime.

Verbum sap

"Coordinate System" = "Grid Reference System" = "Position Format"
in various languages.