Those are the instructions on how to use a Rolex GMT watch as a solar compass:
Via larrybiggs.net (second image via craigboyce.com)
- Both the 12 and the 24 hour hand must be synchronized to display local time
- Method 1: laid horizontally, the dial will head North if the 24 hour hand is pointed towards the sun
The margin of error directly depends on the difference between local official time and actual local solar time. But one doesn't need to get too much in the technical details for approximate urban navigation
- Method 2: if the 12 hour hand is pointed at the sun, the 24 hour hand will point North