Gotum,
You can find this by doing an advanced search, but I just copied and pasted it here for you.
Measuring Bone Pressed Erect Length.
Either standing up or lying flat, hold your fully erect penis perpendicular to your body. Take the “0” end of your ruler and press it against your pubic bone, above your penis. Take the measurement at the end of the penis. This is your bone-pressed erect length measurement.
Measuring from the top has the advantage of not measuring against bone that curves as it goes down, but the disadvantage of pushing into ligaments and the chance of pushing the ruler in under the pubic bone. Pick the method that gives you consistent measurements because the idea is to measure gains.
Non Bone Pressed Erect length.
Either standing up or lying flat, hold your fully erect penis perpendicular to your body. Take the “0” end of your ruler and hold it to where the skin of your penis and the skin of you abdomen form about a 90 degree angle, above your penis. Take the measurement at the end of the penis. This is your non bone-pressed erect length measurement. This one is more difficult to get a consistent measurement.
Hope this helps.
Welcome the thundersplace and the world of PE. Happy gains,