Not a duplicate of Why does Mark use Hexadecimal to communicate?
ASCII can encode a question mark. Its code in hexadecimal is
3F. Since a question mark only appears once per question and most questions would be fairly long (i.e. many characters) why would Mark Watney waste precision (17 positions vs 16) to save on one code (
?, length 1, infrequently used vs
3F, length 2)? Also, it would seem that controlling the rotation in 16ths would be much easier than 17ths as 17 is a prime number whereas 16 positions can be constructed by repeatedly halving the perimeter of a circle. Was this simply dumbing it down for the audience?
First result for "ascii table" on Google:
I see no reason why Mark's ASCII table wouldn't have been at least as comprehensive as this. Unless in the movie universe ASCII is substantially different.