Current measuring device (7)
I believe the answer is:
ammeter
'current measuring device' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for ammeter that I've seen before include "Current-measurer" , "Device that measures the flow of electrical current" , "Instrument that measures electric current." , "Current-measuring instrument" , "Instrument for measuring electric current" .)