A few minutes spent setting up will avoid confusion later
If you're acquainted with the basics of grid systems and how GPS works, you'll appreciate that before your GPS receiver can tell you anything useful you'll need to spend a little time on some basic setting up. Different receivers hide these settings away in different places - look for Setup, Preferences, System or similar and you'll not be far off.
Time
As we've learnt earlier in this series, GPS relies on knowing the time to figure out where you are. You don't actually need to set the clock on a GPS receiver - the first time you turn it on there'll be a protracted initialisation procedure while it figures out which satellites it can see, what time they all say it is and gradually narrows down its location and sets its own clock. What you will need to do is set the correct time zone. In most cases you're presented with a list of countries or regions. Assuming you're in the UK, most receivers will automatically switch themselves between GMT and BST as appropriate.
Grid systems and datum sets
By default, GPS receivers tend to use longitude and latitude (see Part 1 for a fuller explanation). Longitude and latitude works well for navigating oceans, but for more local use you need the information relating to the grid system used for mapping wherever you are. In the UK this means an Ordnance Survey grid reference.
Somewhere in the menus of your GPS receiver you'll find settings for Position Format (sometimes called Coord System) and Map Datum. If you're using a Garmin receiver in the UK, you need "British Grid" as your position format and "Ord Surv GB" as the map datum. Other brands may have "OSGB" for the grid and "GBR36" for the datum. Once these are set, the receiver will give you familiar Ordnance Survey grid references, allowing you to quickly pinpoint your location on a map.
Magnetic or grid North
As well as a choice of grids, you'll also have a choice of Norths. If you choose Grid North, your GPS will align its north with that of your maps. If you choose Magnetic North, it'll agree with your compass. The difference between the two Norths varies over time and with location, so you can set that too. Given that a compass is a vital piece of backup equipment, it makes sense to have your GPS set to Magnetic North too, although using Grid is less of a brainache if you're referring to a paper map.
Measurement units
You'll be presented with a range of options for measurement units, although most riders will be choosing between kilometres and miles for distance and metres and feet for altitude. Which you choose is really up to you - many people find the Imperial units more intuitive, but going metric makes sense given that the grid squares and contours on the map are in km and m. Measurement units can be set to your personal preference of either Kilometres for distance and Metres for altitude or Miles and Feet if you prefer.
Other settings
Once you've got the basics set up you'll have a whole range of options to personalise the settings to suit how you want to use it. One setting that's worth a look is the backlight - lighting the screen up is a big drain on the battery, and turning the brightness and shut-off times down can extend battery life significantly.
