Compensatio (charging to account) was a rather complicated institution in Roman law. The basic idea, however, is simple: when two parties involved in a court case have claims against each other, the claims are not treated separately, but are offset one against the other -- as far as the amounts cover each other. Both claims are thereby paid off, so that the complaint becomes groundless and the defendant can no longer sue for his counter-claim. The complication in Roman law resulted from the different legal procedures connected to the different reasons leading to claims.
Ga…