what is "traditional" about the shapes of specific clubs, while allowing for the progression of technology. The "traditional and customary" rule was originally used to ban the introduction of steel club shafts (patented in 1910), as that material was not traditional for shafts; that specific ban was rescinded in 1924 by the USGA (the R&A would continue to ban steel shafts until 1929), and steel would become universal until the development of graphite shafts whose introduction was less controversial. The "plain in shape" rule was more recently bent to allow for non-traditional driver club head shapes, such as squares, as a compromise to club-makers after imposing and enforcing a 460cc volume limit on these same club heads. Many recently developed woods have a marked "trampoline effect" (a large deformation of the face upon impact followed by a quick restoration to original dimensions, acting like a slingshot), resulting in very high ball speeds and great lengths of tee shots. As of 1 January 2008, the USGA and R&A have settled on a regulation that limits the acceptable "trampoline effect" to a coefficient of restitution (COR)—a measurement of the efficiency of the transfer of energy from the club head to the ball—of .830. Other large scale USGA rulings involve a 1990 lawsuit, and subsequent settlement, against Karsten Manufacturing, makers of the PING brand, for their use of square, or U-grooves in their immensely popular Ping Eye2 irons. The USGA argued that players who used the Eye2 had an unfair advantage in imparting spin on the ball, which helps to stop the ball on the putting greens. The USGA utilized John L. Saksun, founder of Canadian golf company Accuform Golf, as a consultant to set up methods of measuring the unique grooves and determining PING's compliance with the rulings. Saksun, by proposing a cost-effective solution to help PING change the design of subsequent Eye2s, saved PING hundreds of millions. PING subsequently withdrew their US$100 million lawsuit against the USGA. Ping’s older clubs were "grandfathered in" and allowed to remain in play as part of the settlement. However, the USGA has begun phasing in a ban on square grooves in golf. Manufacturers were required to discontinue noncompliant clubs by January 1, 2011. According to the USGA, as January 1, 2010, professional golfers on one of the top tours, or those attempting to qualify for one of the three Open Championships (since then four) will