Profound backing indeed surrounds instrument on display? (6)

I believe the answer is:

speedo

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'display?' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for speedo that I've seen before include "Dashboard instrument (abbr)" , "Mph indicator" , "The clock (in a car)" , "It measures rate of progress" , "Trademark swimming briefs" .)

I've seen this clue in The Times.

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