Non bone pressed vs bone pressed

People say that the ”non bone pressed” is the visible length, i am a bit confused because i can masturbate with the full length of my penis, which obviously means i can see it aswell, so does non bone pressed measurement counts from the beginning of the skin pad? Because otherwise my nbpel is literally 4 inches and my bone pressed is 7 inches, i just feel stupid stressing over this and i hope someone can put my mind at ease a bit, not sure if someone understands me or not lol,

Basically does npbel measurement starts at the skin or does it start at the penis above the skin? Cause i can just push the skin back a bit and still see 6-7 inches of dick. I’m not overweight at all and fairly athletic.