One in charge giving good measure? (5)
I believe the answer is:
ruler
This clue is a double definition.
'one in charge' is the first definition.
(someone who rules)
'good measure?' is the second definition.
(device for measuring)
'giving' is the link.
(Other definitions for ruler that I've seen before include "Leader - line-drawing aid" , "Potentate" , "King, president etc." , "Controller" , "Person in power - can draw a line" .)