Use of a compass supplements navigation from maps, and is best undertaken when required, and not constantly. The degree of error when using a compass in open country is typically about 3–4° and more in scrubby, rocky or thick country. The following precautions should be observed when using compasses:
- Do not use a compass near iron or steel objects. These include steel torch cases, knives, watch bands, tools, steel-framed spectacles, belt buckles, steel pack frames, etc.
- Local deposits of mineral ores may also affect a compass, e.g. over large areas of Western Australia, South Australia’s iron-ore deposits, and sections of the Bogong High Plains in Victoria. If the compass bearing alters significantly from when it is held near the ground to when it is held high, local magnetic effects should be suspected. In this situation, try to move to a location without such effects. If the effect is widespread, one suggestion is to note the bearing on the ground, and the variation at waist height. An additional half of this difference should then be applied to the bearing at waist height.
- Do not use a compass near exposure meters, cameras with built-in meters, or other electronic gear.
- Do not use a compass in close proximity to electric power lines or motor cars.
- The filament of some torch globes, acting as an electromagnet, may deflect a compass needle or affect its polarity if the torch is on.
- Most compasses manufactured for use in the northern hemisphere will not operate satisfactorily in the southern hemisphere and vice versa. This is because the needle is weighted for magnetic dip, which is different in the two hemispheres.