Infinito that was an excellent quetion. Different schools of thought looking at the spin on ball and 70%bs means nothing without knowing which method is referred to.
TBE explained 100ts to 0 ts ( which is middle of ball) and 0 to 100bs ( bottom of ball) my 75%bs backspin would be equal to his 50% bs
I do it a bit different
This is how it was explained to me, 1 way isnt better than another. The key it so be CONSISTENT so you get repeatable results. That is why I use ZOOM setting the spin sometimes to make sure I get it exactly where trying to.
I look at ball same as my putter scale in 5-10% increments top to bottom
0 ts spin = dot at top
25% ts = dot 1/2 between full ts and not moving the dot
50% Dont touch the spin or I call it "dot ball"
75 % bs = dot 1/2 between not moving dot and 100% bs
100 % full bs = dot at bottom
When you move the dot down to where it is just barely touching the swoop I consider that 60% bs
when you have a little gap of white between the top of dot and the nike swoop I consider that 70% bs