this also makes sense anthropologically, since humans seem to have a built in social instinct to compare penis sizes. so if you run out of peer penises, or it is deemed socially unacceptable, one can transfer the instinct into measuring everything else compared to one’s penis.
if this would be a social norm, the standard unit approximation would probably keep increasing incrementally over the years, for social reasons.
“that door is 6 dicks wide”
“I only measured 5,2 dicks wide”
“…”
The speed with which one dick unit would increase per year on average will be called SUE or small unit energy.