With the permission of Goddess Deena, i would like to add some things about JC's method. There are certain things to consider while using it:
A) Method works perfectly when you have a constant dot speed. Unfortunately, rarely you can have breaks with perfect constant dot speed.
B) Method works perfectly speed wise. This means that you have to find the perfect speed for the ball. Half foot more or less changes the whole calculation. It won't work for instance if on a putt we play softly and on the other one we play ramming speed. You need to have the perfect speed for each putt, which is very very difficult as most of you know.
C) The main problem remains on which camera to pick when i want to calculate the dot speed in order to implement the method. Inaccurately has been stated that the best way to do that is to consider the straighter one. I can assure you that you will miss many many putts if you are based only on this camera. The thing is that sometimes straight cameras presenting dot speed much slower than actually is.
D) Another thing that has to be taken in consideration is the green speed, so you have to make tiny adjustments to the method if you play 14 greens instead of 8 for example. Putting speed remain always crucial.
As for the A point, a nice way to use JC's method even with putts with various speeds is to take in account an average speed as a reference. It will work quite well in most cases.