Exclude a possible cause of faulty measurement (4,3)

I believe the answer is:

rule out

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'exclude' is the definition.
(I've seen this before)

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

(Other definitions for rule out that I've seen before include "Dismiss from consideration" , "Eliminate, exclude as irrelevant" , "Exclude from consideration" , "Exclude as ineligible - with drawing stick?" , "Exclude as irrelevant or inadmissible" .)

I've seen this clue in The Globe and Mail.

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