re: 20/20 vision for John Emery

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20/20 is perfect vision.

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Not strictly correct. 20/20 vision means that you can see objects 20 feet away from you as though a regular person sees objects 20 feet away.

While some ranges outside of 20/20 are generally worse (for instance, 20/100 vision means that you need to be 20 feet away to see an object with the same clarity that a normal person can see from 100 feet away; very difficult to imagine a scenario where this is useful), sometimes non-20/20 vision can actually be better for situations where long-distance viewing is needed. For instance, a fighter pilot's ideal vision may well be 20/10 because of the need to identify potential targets or dangers more quickly than normal people.

ETA: As far as playing football goes, I guess 20/15 or 20/10 vision is better, but I doubt it's of substantial tactical benefit. Fixing vision to 20/20 is probably pretty important ( ) but anything "better" would be of dubious value.