I've been volunteered to give a short instructional presentation on a nautical topic. The topic selected is titled "Variation, deviation and compasses
The subject is easy enough but can you think of any answer to the inevitable question of why.
If you hop on a boat today with 4 people you probably have at least 6 GPS
's on board.
Yes the satellites could fall out of the sky half way through our 3 hour cruise or the military could block the signal but can you think of any more likely ways, knowledge of the subject could come in handy.