The intermodulation distortion (IMx) is a mathematical function of F1 and F2.
absolute power
minus
relative
The term relative power, in this example, is referring to the original output power setting of 43 dBm. When stated in units of dBc,
the received PIM power is relative to (is being compared to) the transmitted power level of one test tone.
The difference between the transmitted power (in dBm) and the measured PIM power (in dBm) is the relative power, which is then expressed in units of dBc. This is not applicable in Noise Floor measurements.