A new thought about measurement
This won’t work for girth measurements, but I think girth measurements leave less open to interpretation.
For length, what are we really after? Isnt this all about penetration? Seems to me the most accurate and meaningful measurement would be “penetration depth”. How would you measure this? Any clear cylinder would work, I would think. This would be a bone pressed measurement. In essence, you simply push your dick into a tube as far as you could and mark it. Even more precise, would be to have some kind of plunger your penis could push up the tube. You could have a pre-marked tube. Would give you fast and pretty definitive results.
I only bring this up cause I was thinking about and was wondering if anyone has thought of this, discussed this, tried this, or seen any device that was meant for this.