To use the solar angle to find out direction.
A watch can be used as a compass when the sun is visible to find out directions. To do this, hold the watch flat and then point the hour hand in the direction the sun is visible. Then visualize an imaginary line running from the centre of the watch through a point midway between the hour-hand and the number twelve. This imaginary line will point to the South. Note this rule: Before twelve noon, you have to bisect the angle formed by going anti-clockwise from the number twelve to the hour hand. After twelve noon, you have to bisect the angle formed by going clockwise from the number twelve to the hour hand.
The astronomical reason for this is in the Northern hemisphere, the sun is due south at noon. If at that time of the day, you point the hour hand at the sun, the hand and the number twelve both will point south. Before that time, the position of the sun will be anti-clockwise from the number twelve, and after that time, clockwise. Thus during the 24 hours from twelve noon to twelve noon, the sun will do a complete circle back to its original starting point, but the hour hand will make 2 circles in the same direction around the dial. Hence, the distance the hour-hand travels, and the angle determined by its travel, must be halved. On the Southern side of the Equator the number 12 must be pointed at the sun. The angle between this number 12 and the hour hand will then indicate the North direction.