[Cboldt]

The claim is that there are 10 nerve cells in the retina servicing the fraction of a person's field of vision that occupies the area of an object that is 1/4 the size of the full moon.

It's not an analogy. It's meant to be a precise statement, but made in terms that people who are clueless about arc-seconds can comprehend. Most people can picture "a full moon" without knowing the diameter of the moon either.

[ProtectOurFreedom]

It’s funny, I can deal with arc-seconds, but have a hard time deciphering that sentence.