Eli5 – how does a gmt watch function as a compass by setting the watch to the local time? And is it accurate?

Question

I have seen 15 different YouTube videos on finding north using a gmt watch and I’m confused how accurate or useful that even is.

In: 1

Answer 1

The thing to understand is that the sun does a full lap of the sky each day as the Earth rotates underneath it. You can’t easily see that full lap unless you are in the arctic circle in summer, because the sun is below the horizon for part of the lap.

So you can work out the time by the angle between the sun and the compass – at 12 local time it will be due north or south, at 6 it will be due east or west.

The really neat thing is that the hour hand on an analogue clock does two full laps in a day, so you can use the angle of the hour hand to work out the angle the sun should be relative to north.