Tool that counts for auditor (4)
I believe the answer is:
adze
'tool' is the definition.
(adze is a kind of tool)
'counts for auditor' is the wordplay.
'counts' becomes 'adds' (adding is a kind of counting).
'for auditor' indicates a 'sounds like' (homophone) clue.
'adds' is a homophone of 'ADZE'.
'that' acts as a link.
(Other definitions for adze that I've seen before include "Carpenter's tool sounds mathematical" , "One might cut" , "Dresser" , "Daze with a sort of axe" , "Carpenter's tool sound mathematically capable" .)