You can count on them
'you can count on them' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for abaci that I've seen before include "You can count on them" , "Counting devices" , "frames" , "They once reckoned" , "on which people may be counting?" .)
'you can count on them' is the definition.
(I've seen this in another clue)
This is all the clue.
(Another definition for fingers that I've seen is " Digits".)