Use StA #10 for practice. Flop/pitch it onto the green, then putt it back off again. Rinse and repeat.
Make sure you flop/pitch onto a part of the green that is totally flat, for best measurements. Do it in a ranked round for proper green speed, do it in practice for VF and slower greens.
Note that wind does effect flops, so try getting a round with as little wind as possible, or sidewind if you mostly want distance.