Made sure when patterned so (7)

I believe the answer is:

checked

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'made sure' is the definition.
('check' can be a synonym of 'make sure')

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

Can you help me to learn more?

(Other definitions for checked that I've seen before include "Patterned with alternating squares of colour" , "Restrained" , "Verified, passed inspection" .)

I've seen this clue in the Sydney Morning Herald.

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