Look through the FAQs - http://www.wgt.com/forums/t/559.aspx
You have to gauge the speed, distance, and amount of break, if any..
The putting stroke meter gives you several ranges. Just roll the center wheel on your mouse to scroll through t he stroke distance scales available to you.
If you're using the Stater putter the stoke scales should be 30 feet, 60' feet 150' feet and 300 feet.
If you use the 30 foot scale and take and 'ding' a stroke using 1/2 the meter the putt will go about 15 feet if the putt is flat.
WGT has an accessory called Putter Pal that divided the putt stroke meter into 10% segments, or you can make your own on paper and attach it to your computer screen.