Grover Rotomatic 406C6 mini locking guitar tuning machine heads make quick work of tuning. With a gear ratio of 18:1, these locking tuners give you all the benefits of standard Rotomatics - plus the positive locking of Grover's internal cam post. Insert your string through the string hole, pull to tension by hand, and start to tune. As you begin tuning, only the locking cam in the string post turns. The string post begins to turn once the string is locked. In under one string post revolution, you'll be in tune. And you'll stay in tune, with Grover's Rotomatic 406C6 locking guitar tuning machines.