Thank you for the initial responses.
Whopity I've just had a look at the wind side of the flight computer. Like you say, it quite clearly states at the top that the indication given shows drift. Therefore the "wind down" method would appear to be the one to use. Thank you.
FlyingForFun The "wind up" method can certainly be a little bit quicker. If memory serves me right there are questions in the PPL examinations that involve making calculations backwards to come out with wind speed and direction, etc. I'll have to pull out my computer at work and have a play when I get the chance.