On Wed, 26 Dec 2018 07:48:43 +0100, Paul Schlyter
wrote:

On Tue, 25 Dec 2018 07:33:29 -0700, Chris L Peterson
wrote:
On Tue, 25 Dec 2018 10:46:25 +0100, Paul Schlyter
wrote:

But if the distance is irrelevant, why not perform the division
and
say 0.67 instead of 20/30? Or at least 2/3 instead of 20/30? After
all it means that the person with 20/30 eyesight has 2/3 or 0.67
of
normal visual acuity.

It's just convention.

An unnecessary convention which should be removed.

Fine, take it up with the ophthalmological community. But it works,
people are comfortable with it, and I don't imagine it's likely to
change.

Suppose that I, instead of saying "it's 5 degrees outside", suppose
I would say "it's 35/7 degrees outside". It's the same thing, but
you'd probably ask why I involved that 7 in the temperature, and then
I would reply "it's just convention"... See?

If it were convention, it would sound normal to us and we'd use it
comfortably. That's pretty much what "convention" means.