You can master long putts by working on your distance control, which is directly related to your rhythm.
Too often, we fail to take the putter back far enough on long putts, and instead take a backswing which is not long enough and then “hit” the ball to compensate, rather than stroking the ball smoothly. This results in poor distance control as a result of poor rhythm.
A great tool to assist in improving your rhythm is the Frog Stick, our practice putting device which really helps give you the confidence to take the putter back far enough, adding a feeling of flow to your stroke, ensuring you are putting in the correct plane, as well as assisting with alignment.
For a scientific take on tempo and backswing length in putting, see Robert Grober “Resonance as a Means of Distance Control in Putting”. He has information on proper tempo (defined as backswing time to downswing time = 2:1), and also notes that, given a constant backswing to downswing time (2:1), the length of the putt is related only to the length of the backswing. In other words, to change putt distance, only change your backswing length, and keep your tempo the same. I think Frank was getting at that in his column when he says that most golfers change their tempo and thus lose distance control.
Rhythm: This past weekend winners in both LPGA and PGA extended index finger down the shaft while putting. However, both lost rhythm on shorter putts and missed badly, one that could have sealed his victory in regulation, the other who could have closed the deal earlier in her playoff. Both won but I felt both needed to study your Fundamentals of Golf.
franklygolf 
For a scientific take on tempo and backswing length in putting, see Robert Grober “Resonance as a Means of Distance Control in Putting”. He has information on proper tempo (defined as backswing time to downswing time = 2:1), and also notes that, given a constant backswing to downswing time (2:1), the length of the putt is related only to the length of the backswing. In other words, to change putt distance, only change your backswing length, and keep your tempo the same. I think Frank was getting at that in his column when he says that most golfers change their tempo and thus lose distance control.
Rhythm: This past weekend winners in both LPGA and PGA extended index finger down the shaft while putting. However, both lost rhythm on shorter putts and missed badly, one that could have sealed his victory in regulation, the other who could have closed the deal earlier in her playoff. Both won but I felt both needed to study your Fundamentals of Golf.