Compasses , along with the appropriate map and their correct use, are invaluable for cross country navigation. Global Positional Systems are becoming more popular in bushwalking circles. The price of them has decreased considerably over the last 5 years. In certain locations and vegetation types such as deep valleys and rainforests they are useless. Combined with good map and compass navigation, they may be a useful accessory to have.
Altimeters are a good aid when it comes to rainforest navigation or snow covered country.
To be used correctly they need to be calibrated from a known position from a map. There are two basic types, one is a wrist-worn combination watch eg. They can also be used in determining the barometric weather trends. It is important to note that barometric pressure may change considerable during the day due to fronts, highs or lows, and should be calibrated a few times a day. When a route has been planed it is fairly easy to work out the total distance of the walk.