On Tue, 01 Jan 2019 09:15:14 +0100, Paul Schlyter
wrote:

On Mon, 31 Dec 2018 09:26:42 -0700, Chris L Peterson
wrote:
Don't you see the beauty in performing that division?

Nope. It discards useful information. It's like characterizing a
aperture
telescope by focal ratio, and not providing the focal length and
aperture.

If all telescopes always had the same focal length it would be
practical to do that. Then the aperture could easily be calculated
from the focal ratio and the implicit focal length. Now, this is not
the case of course, but in the case of visual acuity tests the
Snellen chart is always at the same standard distance.

That's what you're missing. The test is NOT always performed from the
same distance, and as a result, the distance is a meaningful part of
the test reporting.

A patient with 6/6 vision and one with 3/3 vision may have
significantly different visual acuity; if you normalize them to 1.0,
you lose that distinction.

Did you ever see any visual acuity report giving the result 3/3? (is
that in feet or meters btw?)

Yes. That's a common result in Europe (and it's meters).

Btw, how do American eye doctors give the strength of corrective
lenses, or of any lenses? In metric diopters like in Europe? Or do
they have their own diopter scale based on feet instead of meters? Or
do they just give the focal length in feet?

Diopters. Always. (By definition, a diopter has units of reciprocal
meters, so could always be considered "metric".)