Auditors multiply it by itself 3 times to match the old measure (5)
I believe the answer is:
cubit
'old measure' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for cubit that I've seen before include "distance" , "Elbow-to-finger measure" , "Biblical measure of length" , "two such might have been in the yard" , "Ancient unit of length based on the length of the forearm" .)