Jim Hardy, 63, is a former Tour pro, a noted architect (Jacobsen-Hardy Course Design) and a top teacher whose students include Olin Browne, Tom Pernice Jr. and Paul Azinger. Every year Hardy also teaches a dozen two-day seminars to PGA golf professionals. His first instruction book, The Plane Truth for Golfers, came out last summer and was a hit. A DVD version ($100; 800-363-3212, was just released.

Why do you think so many golfers have taken to The Plane Truth?
Because it makes the case that there is not just one but two sets of golf fundamentals. If you identify which type of swing you have, you will know whenever you hear golf advice being offered whether it pertains to you or not.

Explain the difference between a one-plane and a two-plane swing.
How the arms swing relative to the body turn is the decoder ring. Your body pivots and your arms will either swing on the same plane—a one-plane swing—or they'll swing up and onto an entirely different plane.

Which is Tiger?
Tiger is certainly a one-planer with the irons. But with the driver, he has been standing too upright and lifting his arms up and out a little too much on the backswing to really be classified as a one-planer.

Is one type better?
I have a slight preference for one-plane. A two-plane swing will eventually hurt either your lower back, your left shoulder or your left elbow if you can swing at speeds over 100 m.p.h., and while a two-plane swing is easier to learn, it requires timing, tempo, rhythm and balance, and that's a daily thing.

What's it like to be the teacher who the teachers come to and learn from?
It's kind of humbling.

Finally, what does the DVD set have that the book doesn't?
More pictures! The whole thing is a picture. There are three discs that cover the book, plus a fourth of drills. Also, you can punch up only the stuff you need through the index. It's easy to navigate through.