Graph Tech Ratio 4-In-Line Bass Y-Style Button calibrated machine heads incorporate different string gauges into the tuning equation. The Graph Tech PRB-4400 is a right-handed set of Ratio calibrated machine heads for bass guitars that use a 4-in-line configuration. Every string reacts the same to any tuning adjustment, delivering predictable, precise tuning, on every string. With ratio, a half turn is a semi-tone. Graph Tech Ratio tuners use a double envelope gear design with a hardened steel gear that makes them amazingly smooth and super strong.