Graph Tech GTR872 Ratio Locking Machine Heads for Electric/Acoustic Guitar (6-In-Line)RATIO patented gear technology RATIO Calibrated Machine Heads incorporate different string gauges into the tuning equation. From Low E to High E 39: 1, 24: 1, 20: 1, 35: 1, 20: 1, 12: 1. We balanced the gear ratios to each string simplifying the tuning process. With RATIO, a half turn is a semi tone! Every string reacts the same to any tuning adjustment. Predictable, precise tuning, on every string. The PRL 8721 and PRL 8731 are right handed sets of