Motor’s gauge deep, so adjusted (6)
I believe the answer is:
speedo
'motor's gauge' is the definition.
The definition suggests a singular noun which matches the answer.
'deep so adjusted' is the wordplay.
'adjusted' indicates an anagram.
'deep'+'so'='deepso'
'deepso' with letters rearranged gives 'SPEEDO'.
Can you help me to learn more?
(Other definitions for speedo that I've seen before include "one gives you the going rate" , "Mph indicator" , "reading from this" , "The clock (in a car)" , "It measures rate of progress" .)