Did you try a Payroll Simulation with the "Display log" box checked?
Open the log and drill down to PCR X010 (by selecting the folders, one at a time)
Once you see X010 (our version is ZX10), double clic on the Function PIT, on the PCR X010 or on the parameter P01 associated to the function and you will be able to see the Input Table, the processing in the PCR, and the Output
If you want to learn more about processing within a Function, or about an Operation used within a PCR, use t-code pe04 as suggested by Pharda.
If you want to learn more about the PCR, use t-code pe02.