No, not that cheap GPS. This one:

IMAG0164I bought myself a Garmin Dakota 10 last year to use for road cycling. It does a great job for that - crucially, the basic UK road map it comes with is good enough that if you pre-load your route into it, you can usually see which way to turn at a junction without having to stop and consult your paper map. This really helps keep up the momentum. It also happens to run on AA batteries, which is handy as I carry a full spare set of those to feed my bike lights anyway.

However, setting off last Friday for a weekend in the Lake District, I threw it into my backpack just in case. It turned out to be extremely useful as we climbed Weatherlam in near-zero visibility caused by fog. You have to dig in to Settings > Position Format:

Settings screenWhat to select for OS map referencesAnd select "British Grid" and "Ord Srvy GB". Having done so, you can add the "Location" field to the compass view, and it will tell you your OS grid reference:

Compass screen with OS grid referenceIn the above example, "SP" is the OS grid square, and the two rows of numbers are the X and Y references within that square (I've blacked out most of the numbers so you can't see where I live).

This is very useful when your best efforts at map-reading start to come unstuck on the ground. Some semi-jokey remarks were made in our group about it being cheating, but I wouldn't go out without a GPS now - it could literally be a lifesaver if you get lost or stuck, and you can get one for less that £100.

Obviously, the reference is only as good as the accuracy of the GPS (on mine, you can tap the bars showing the satellite signal strength to see how many feet/metres it thinks it's accurate to) - but I certainly found the first three digits of each co-ordinate to be close enough for my purposes. What you have to be wary of is placing too much reliance on the difference between readings taken a few minutes apart, because the inaccuracy could be big enough to make it seem like you've gone the opposite way to what you actually did.

The compass, incidentally, is useless - slow to update and very dodgy [Update: A friend writes: The compass in cheaper GPS units often isn't a dedicated chip. It only works based on your direction of travel as reported by GPS co-ordinates. So you need to walk in a straight line for a few yards with the GPS unit held in front of you for it to do anything resembling the right thing.]. Just use a proper magnetic one instead.

Also, I can heartily recommend having a laminated OS map. "There's no such thing as bad weather, only bad equipment".