Wait... so to signal "17" you put your fist up, then down, then up, then down, then up, then down, then two fingers???
I have taken 10's of thousands of people diving and I have seen just about every hand signal for air remaining, but that one would have left me looking like a confused Labrador Retriever thinking you were doing the Macarena. Then I would have looked at your gauge myself because you clearly can't be trusted to give me something approximately accurate.
Divers with digital gauges were the worst. They can't just signal "17" or even 1,7,0,0, the have to give you 1684. And half the time would get confused in the middle of it. It would be 1,5,1,5,2,4,3...frantic waiving of the hand back and forth to erase the previous answer, 1,5,2,3,5,2,1...3,5,2. Followed by a look of triumph.
WTF? Just show me. Oh you can't, because you have an Oceanic data mask.
Ahhhh, guiding dives. So much fun!