Although it is common practice to compare different piston engines and their performance potential by referring to the engine displacement or swept volume this does not give an accurate reading of an engine's capabilities. According to A C Lovesey, who was in charge of the Merlin's development,[nb 3] "The impression still prevails that the static capacity known as the swept volume is the basis of comparison of the possible power output for different types of engine, but this is not the case because the output of the engine depends solely on the mass of air it can be made to consume efficiently, and in this respect the supercharger plays the most important role."[16]