Each revolution of the tool results in 3 revolutions of the tuning key. Ergonomically designed to fit in the palm of your hand, operation is a smooth circular arm-hand motion. So this winder is comfortable and very, very fast. There is also a built-in bridge pin puller. Designed for use on sealed-gear tuning machines that have a good gear ratio and require low torque (Snake does not work well on mandolin, classical guitar or similar open-gear style tuners). There are two models - "green" for 3-on-a-side tuning machines with larger buttons and "purple" for 6-in-line tuning machines with smaller buttons. If you appreciate nicely designed human powered tools, you will like this winder. Everything does not require batteries or an electrical outlet to be effective.