pmp stretching length measurement

[Asphyxia]

im transitioning to pmp from andropeyronies, and in andropeyronies manual book i can measure the length by the rods, however in pmp i cant tell the length, i guess i can measure it but i dont know how deep my glans are in for me to measure, so how do you know the length of the stretch?

also in the manual i read it says to start with a pulling force between 200 and 1100 grams, can those be translated to length?