Perhaps you did not understand what I said. You get the rating 20/20 when you can see at 20 feet what others can see at 20 feet. 20/40 when you see at 20 what most can see at 40. If you were to stand 3/4 of the correct distance from the chart and see what normal people see at 20 feet, your vision would be 15/20. Sure, it isn't standard or anything, but it exists.
Hence the chart or device is calibrated to a standard of 20 feet, 10 feet in rare cases. Sure, it exists mathematically as a ratio, but it is not used in practice. You don't stand 3/4 the correct distance from the chart unless you and the eye doctor are autistic.
I hate human stubbornness, why are you even arguing this?
I assume originally he meant 20/15, because he claimed his eyesight was very good.