Gauge poetic rhythm (5)
I believe the answer is:
I believe this clue is a double definition.
'gauge' is the first definition.
(I know that meter is a gauge)
'poetic rhythm' is the second definition.
(meter is a kind of poetic rhythm)
(Other definitions for meter that I've seen before include "Device for measuring and recording" , "Measuring device as for electricity usage (5)" , "Device for recording, say, usage (5)" , "Poe sometimes used this" , "Gauge" .)