It is now common knowledge that string tension exerts a longitudinal compression on the guitar neck. This compression subtly alters the neck’s shape—sometimes enough to cause fret buzz. For a long time, the “old school” struggled to understand why leveling frets without actual string tension in place often led to imperfect results, requiring further touch-ups after reassembly.

Leveling the frets with the instrument in playing condition—at least with the strings on, tuned to pitch, and the neck held straight—is a major step forward. Even better results come when the leveling is done under full playing conditions: with strings on, relief set, and the instrument held in a vertical playing position. In this ideal state, the neck is shaped exactly as it will be when played. After crowning and refinishing, the neck will return to the same profile it had during leveling, ensuring optimal accuracy and performance.

Today, luthiers and players around the world are witnessing the benefits of this fret leveling technique. The image above made history. It has been featured on Rectify Master’s front page since 2010, seen by hundreds of thousands of professionals and enthusiasts, and discussed widely in forums. Though simple, it is a powerful image—it distills the essence of fret leveling with strings on into clear, intuitive visuals that helped countless people instantly grasp the concept and embrace it.

Also worth noting:

• The straight (non-adjustable) version is patented in Japan: JP5030186B2
• The adjustable version (which also works straight) is patented in:
    – USA: US9224369B2
    – Europe: EP2608194B1 (including UK, DE, FR, IT)
    – Japan: JP5938783B2