I believe that one of the problems here is mixing “everyday” terminology with precise measurements. And the world is full of these reporting problems.
(And another is that we all know that the penis varies in size with all sorts of external and internal conditions. I’m not going near that aspect… … .!!!!
If we go “back to first principles “… … … … … ..
Built into any reporting of any measurement in the scientific and engineering world is a very basic understanding that if something is said to be 6 inches, that in the absence of any other information, we are to assume that there is a range of lengths that could reasonably be called “6 inches”, and that equates to “plus or minus half of the smallest dimensional unit being quoted “.
Thus in this case, 5½” to 6½”.
Perfectly reasonable for an everyday discussion of penis length around the office water cooler, or these days over video link.
And if we report something else’s average as 5.1”, naturally the same rules apply.
But the outcome is very different. And in the context of the human penis, and an ordinary school ruler, ridiculous. ( Yes, I know they are not “rulers”, )
Here, the smallest subdivision is 0.1”, and the implied allowable range is taken, therefore as 5.05” to 5.15”. In the context of an average penis circumference, or girth, utterly meaningless… … … … .
(BUT, if you are measuring today, and you get 5.1”, and you are looking for a trend, then by all means write it. down, and use it for your own running average.)
Penises must be some of the most difficult objects to measure with any degree of repeatability and confidence.
So, when quoting “Averages”, best not compound the repeatability difficulties by striving for too many decimal points !!!