On Mon, 24 Dec 2018 09:26:32 -0500, Davoud wrote:
20/20, or metric 6/6 = 1. It's explained at
https://en.wikipedia.org/wiki/Visual_acuity#Measurement.

Ok, so it measures the visual acuity at a distance of 20 feet. But
wouldn't a measure of (practically) infinite distance be more
interesting to skywatchers? No stars are only 20 feet away.