MulliganWilly: i think that's 'very fast' or something.. well lets say its 20ft ahead but you see like a elevation of +10 inches.. well what i noticed is that for each inch of elevation add 1ft for putting distance.. so for that you'd go.. well its a bit less than 20ft with the very fast..
No! Very fast greens give a little less than 20% reduction in required putting power. For your conditions above, my mental calculation goes like:
'20 ft, - 4 ft = 16. Add 1.5 ft to be sure = 17.5. Now add the 10 for elevation increase, and we have 27.5 ft of power needed.
Your putt of 19. something ft would end up 5 ft short, give or take.
Please trust my numbers - they've worked over hundreds of rounds.