Which of the following would not help determine compressor displacement?

Determining compressor displacement requires understanding the parameters that directly influence the volume displaced with each cycle of the compressor. The volume displacement of a compressor is primarily determined by the dimensions and configuration of the pistons and cylinders.

The length of the piston, while it does have implications in certain mechanical aspects, does not directly affect the volume displaced by each stroke of the compressor. Displacement is calculated based on the area of the piston and the stroke length, which refers specifically to the distance the piston travels within the cylinder. The diameter of the piston contributes directly to calculating the area that the piston sweeps through, while the number of cylinders adds to the overall displacement by accounting for each cylinder's contribution. Similarly, revolutions per minute (RPM) indicate how frequently the compressor operates but do not, in themselves, affect the physical displacement per cycle.

Thus, the length of the piston stands out as a factor that is not directly tied to the calculation of compressor displacement in the same manner as the other listed options.