Complex sentence: It is important to use the same absolute units for T and T c as well as for P and P c; the unit system used (K or R) is irrelevant because of the usage of the reduced values T r and P r.
Split into simpler sentences: It is important to use the same absolute units for T and T c as well as for P and P c. The unit system used (K or R for T) is irrelevant because of the usage of the reduced values T r and P r.