The effect of this arrangement was that the gear ratio between an engine and the output shaft depended on how many engines were driving the transmission. Gear ratio selection was accomplished not by "changing gear" in the conventional sense, but by filling or draining the hydraulic couplings to connect or disconnect the engines from the transmission. With only one hydraulic coupling filled with oil and the other three engines disconnected and their respective input shafts to the transmission locked by the one-way clutches, the single engine drove the output shaft through an effective gear ratio of 4:1. With two engines driving, the effective gear ratio was 2:1; with three engines, 1.33:1; and with all four engines, unity. In other words, the effective gear ratio of the transmission was the inverse of the number of engines driving it.