The right doctor assembled emergency room gauge (11)
I believe the answer is:
thermometer
'gauge' is the definition.
'the right doctor assembled emergency room' is the wordplay.
'right' becomes 'r' (common abbreviation).
'doctor' becomes 'mo' (medical officer).
'assembled' becomes 'met' ('meet' can be a synonym of 'assemble').
'emergency room' becomes 'er' (abbreviation popularized by US TV series).
'the'+'r'+'mo'+'met'+'er'='THERMOMETER'
(Other definitions for thermometer that I've seen before include "Temperature-measuring instrument" , "Temperature gauge" , "Instrument with mercury or alcohol" , "Temperature measure" , "Device measuring temperature" .)