On Mon, 24 Dec 2018 22:04:24 -0600, hleopold
wrote:
If the numerator is always 20, what does this 20 mean? Is 20/20 in
some way different from, say, 25/25 or.30/30?

As I understand it, you should be able to see at 20 feet as the
average
person would see at 20 feet. (An average person with good eyesight
of
course.)

If you are shown to have a 20/30 in your right eye it means that
you see at
20 feet is like that average person would see at 30. In other
words,
your eyesight is not that great.

But what's the point of always having 20 as the numerator? Why not
instead perform the division and say 0.67 instead of 20/30? Or, if
you prefer common fractions, 2\3? After all 2/3 is equal to 20/30.