Features This is an entire Sperzel locking tuner, with an added mechanism to flip between two pitches set by the fine tuning knobs. The tuner is completely universal, appropriate for both right and left usage. Installation If you already have Sperzel tuners on your guitar, the install is ridiculously straight forward. Simply remove your existing tuner and replace it with the D-thing. Install complete. I installed it on a guitar with a reverse headstock, so I had to reverse the tuner. To do this, simply use a flathead screwdriver to remove the tuning key, pull the key, collar, and washer off the post, slide the post/gear assembly out the opposite side, and perform the reverse to install it on the other side. Usage The D-Thing is an absolute marvel of engineering design. The flip mechanism works by locking the tuning peg into a short range of motion. To set it up, you back out the find tuners all the way and tune the guitar. You then push the locking mechanism all the way up (to the E side) and lock it with the small locking lever. Next, you turn the tuning peg until the mechanism is all the way down (to the D side) and check your tuning. If it is flat, you turn in the D fine tuner until you reach the correct pitch. If it is sharp, you turn in the E fine tuner, unlock the mechanism, tune the string, lock it, and readjust. Once you have it dialed in, you use a standard screwdriver to lock the fine tuners in place. Performance This is dead simple to use. Once the mechanism is locked, it restricts the range of the tuning peg to between the two stops the fine tuners set. If you need to tune, you unlock it and tune up. Dirt simple. Overall A positively brilliant design that builds upon an already rock solid tuning machine. I give it five out of five heavy metal kitties. Thanks to Mike (eaeolian) for selling this to me. Unfortunately, it wouldn't operate correctly on his guitar: the angle at which his tuning machines are mounted keeps the locking mechanism from operating at it's full range of motion.