CUSP (Cumulative Sum of _P_oints) is the sum over all rounds of the player’s total winning points at the end of each round. Note that winning points at any round is the total sum of wins and jigos and does not include free wins or points gained by sleepers.
If two players start off on the same McMahon score, and end up with the same CUSS (having played all games) then their CUSP will also be the same. This follows since at any round McMahon score is equal to initial McMahon score plus winning points up to that round. So one cannot sensibly use both CUSS and CUSP as first and second level tie-breakers. CUSP is easy to calculate by hand and is therefore recommended for use as the tie-breaker in small tournaments.