In reply to LJJ77:
You obviously know about GPS, I haven't got one. It seems to me that you need to do more judging yourself. What if the whiteout is before the summit. Walking up to it will be as hard as walking down from it as in a whiteout you can go down when wanting to go up just like that.
I know some people share the grid reference to get off Ben Nevis at the summit, probably in this case and many like it you are looking at 2 grid references for starters and accurate judging of distance.
If you are in a whiteout in my opinion your most important skill is pacing as you really do not know up or down hardly anymore .This assumes you already know how to read a map and set a compass pretty well.
Therefore if you cannot do map or compass well you must know where you are on the way up all the time as practice. Any point you cannot find where you are and some pacing to test it fails, seriously consider going down for somewhere safer to get it learnt on.
I am often a bit clumsy without pacing as I can find cols and spurs everywhere, but a bearing is useless if you are in the wrong place except to prove you are in the wrong place.
For pacing test how many steps you take for 100m and carry pebbles to remember your count to 1000m. 1000m is a surprisingly short distance on a Munro ridge.
I don't see how a GPS can help somebody who cannot do map reading well already. If something goes wrong and the GPS told you where you are then surely you really do not know where you are.