Figure it's a double-cross (6)

I believe the answer is:

twenty

I'm a little stuck... Click here to teach me more about this clue!

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

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

(Other definitions for twenty that I've seen before include "Cardinal" , "No. between 5 and 1 on dartboard" , "One score" , "Number" , "This twice denotes normal vision" .)

I've seen this clue in the Evening Standard.

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