ChrisG wrote: Interesting comment, your right I suppose, but I would be interested in your advice on navigation with zero viz
Sorry, that clearly came across as a bit cheeky!
The basic skills you need are:
Keep track of where you are on the map.
Plan a series of legs to get you to your destination.
Take a bearing of the map.
Walk on the bearing.
Estimate distance travelled by pace counting and/or timing.
Identify features on the map which you should be encountering on each leg (including knolls, cols, spurs, re-entrant changes in slope angle and direction) and check these off as you go.
GPSs are great, but as you discovered a back-up is essential!
This is a good book on the subject
http://micronavigation.com/the-book/ , but going on a one or two day course would get you off to a good start, and practise lots, even on days when you can see where you are going!