Ball Compresion is probably the most misunderstood measurement in golf ball design. Many people have no idea of what compression is and what it means.
In the early days of golf, the term compression was originally used as a measurement for golf ball quality. It was actually used to reference the tightness of the windings around the center core of a three piece ball - the tighter the windings, the better the ball performed. This created a long-standing perception that compression affects golf ball distance and performance.
Because golf ball technology uses newer heat-resistant threads with newer and better winding equipment for three piece balls, golf ball compression has become merely a condition of feel. And now with the availability of the consistent quality of a two piece ball, compression as a measurement of quality is just about obsolete.
Today the word "compression" in the golf ball industry relates to a value expressed by a number in the range from 0 to 200 that is given a golf ball. This number defines the deflection that a golf ball undergoes when subjected to a compressive load. Compression simply measures how much the shape a golf ball changes under a constant weight.
As golf balls come off the production line, all three-piece balls and some two-piece balls are measured for compression and rated. A standard weight is applied to each ball - one that doesn't compress is rated 200; a ball that deflects 2/10ths of an inch or more is rated zero. Between those two extremes, for every 1/1000ths of an inch that the ball compresses, it drops one point from 200 and the compression rating is then established.
Most balls have compression ratings of either 80, 90, or 100; the lower the compression, the softer the feel. Not every ball marked 80, 90, or 100 is exactly that rating. The actual rating can fall roughly within 3-5 points on either side of 80, 90, or 100. Any balls that fall out of this range are usually discarded, sold as range balls, or sold as X-outs.
There have been several published texts to prove that golf ball compression relates more to feel and your own superstition than its performance. The conclusions were, if you take different rated golf balls which have the same construction, aerodynamics, and cover material, and use an automatic golf swing machine such as the Iron Man, the yardage difference between the balls hit were negligible, less than two yards