Must I have one?
Yes: if you leave it behind, you'll hit a whiteout on the Cairngorms.

How do I use it?
Read the instructions and practise carefully in the park. Or go on a navigation course somewhere like the Plas y Brenin National Mountain Centre in Wales.

Common mistakes?
Using it back to front, then walking the wrong way: with luck you'll see the cliff before you're airborne.

Important features?
Big base plate, bezel you can turn with gloves on, luminous needle. Good damping, so the needle settles fast.

Why Silva?
That's the Swedish company that invented it in 1932. Some call them protractor or flatbed compasses, because Suunto makes them, too.

Suunto? Swedish again?
Finnish. Navigation's very important to the Scandinavians.

Ah, the trackless tundra?
More like Major Ernst Killander, who took Stockholm's deprived youth into the forests in the 1920s.

Do I want to hear this?
The healthy new game was finding your way from A to B, aka orienteering. And it's hard to use a compass, map and protractor when you're running.

So Silva built the compass on to the protractor?
That's it. For pinpoint stuff, you still need a traditional prismatic compass and separate protractor, but the Silva is used by most walkers and explorers these days.

An arm and a leg?
Between £11 and £60: the widely-used Silva Type 4 is £29. Prismatic pocket compasses cost £40 to £60.

Do say:
Allowing for magnetic variation, a bearing of 230 degrees will take us straight to the Dog and Duck.

Don't say:
Please, sir, why does this red needle keep moving about?