One of the issues that we observed with traditional single length iron sets was that the lower lofted clubs sometimes had peak shot heights that were too low and the higher lofted clubs were peaking too high.
Tom Wishon had the clever idea of incorporating progressive offset in to the Sterling Irons®. This offset puts the center of gravity a little farther back from the shaft bore centerline which can help increase launch angle.
This helped solve the problem of too low of shots with the lower lofted clubs.