GPS

Using a GPS in Great Britain

before we use a GPS we must set the GPS to recognise Great Britain's data. We could use Longitude and Latitude

however it is much easier and more recognised to use the British National grid

set the time zone for GMT (or other if GMT is not an option)

GMT has been replaced by UTC
GMT - measures the earths rotation
UTC - Coordinated Universal Time - is based on atomic measurements and has the accuracy needed for GPS to work

set the map data to OSGB

OSGB uses the familiar British national grid using 100 Km squares rather than the default Longitude & Latitude. See the table on the correct use of the British national grid below.

set the map datum to WGS84

OSGB is drawn using a datum of WGS84

set the North to Magnetic

this allows you to use the GPS without having to worry about the setting the magnetic bearing every time you use it.
(remember to also set the variation to 005 deg.)

set the unit

you will most likely want to use metric meters as you standard unit (as this is used on OSGB maps)

Remember what the grid reference should look like

The OS GB uses two letters and then four figures to get to a 1KM square
eg. MN 166713

see below

How to use the 100 kilometre squares

used with the British National Grid

Britain is divided up into 100 KM squares

these squares are given two identifying letters

to give an accurate grid reference

give the grid square
followed by the numerical grid number

an example of this

For a location on Ben Nevis summit

we would use the grid square

followed by the conventional six figure reference

MN 166713
(locating the 100 Km square & the actual reference)

It is not good enough when using a GPS to use a six figure map reference such as 166713

We must use the lettered 100 KM square
we can not use the grid reference and the number of a map e.g. 41 / 166713

For a GPS location on Ben Nevis summit

we would use the reference

MN 166 713

but this reference would be for a 100 meter square (a big area on Ben Nevis)

a GPS is capable of considerably narrowing this down

a reference of MN 16650 71350
is accurate to 1 meter

considering the average GPS is well capable of getting to within 20 meters in normal conditions we should aim to use 12 figure references to capitalize on this is a distinct difference

approaching the summit
of Ben Nevis