I recently read that if you're in the northern hemisphere and have an analog watch, then you can point the hour hand at the sun and know that a south line lies between (bisection) the hour hand and the 12 o'clock position:
Apparently the trick works in the southern hemisphere as well and needs to be adjusted for day-light saving (image taken from Wikipedia):
I would like to know the reasoning behind this trick, and would like to know if the trick can be applied to tell the approximate time provided I only have a Brunton compass.
I made an illustration if it helps:
The basic idea is that the sun is due south at (local solar) noon in the Northern hemisphere. The correspondence between civil time (which your watch presumably shows) and local solar time is quite problematic depending on where you are in the world. In Madrid, Spain in the summer it is over two hours off. The factor $2$ (bisecting the angle) comes from the fact that the hour hand goes around once in $12$ hours and the sun once in $24$ hours.