Indicates number of imperial units (about zero) (6)
I believe the answer is:
points
'indicates number' is the definition.
'points' can be an answer for 'indicates' ('point' can be a synonym of 'indicate'). I am not sure about the 'number' bit.
'of imperial units about zero' is the wordplay.
I cannot really see how this works, but
'of' could be 'o' and 'o' is found within the answer.
'units' could be 'pints' (pint is a kind of unit) and 'pints' is present in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for points that I've seen before include "Directions on compass" , "Tips" , "Precise locations" , "Railway track with two movable rails" , "Heads" .)