The EVH D-Tuna® is a unique patented device that enables players to drop the E to D and back, in an instant. D-Tuna has been standard equipment on Eddie Van Halen's personal guitars as well as signature series locking tremolo-equipped guitars since the early 90's. Since then thousands of D-Tuna's have been sold all over the world. D-Tuna is proud to be endorsed by many professional players such as Warren DeMartini (RATT), Michael Wilton (Queensryche) and Dave "The Snake" Sabo (Skid Row) just to name a few. Bottom line... It's simple to use and it works.