RATIO patented gear technology. RATIO - Calibrated Machine Heads incorporate different string gauges into the tuning equation. From Low E to G - 48:1, 36:1, 25:1, and 23:1. 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 PRB-4401 is a right-handed set of RATIO® Calibrated Machine Heads for BASS that use a 4-in-line configuration. In order to achieve higher gear ratios, Ratio are the world's first machine heads using a double envelope gear design with a hardened steel gear. Amazingly smooth and super strong.