For this cube, what's subtracted from vertical measurement when it's minimised? (5)

I believe the answer is:

eight

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'for this cube' is the definition.
(8 is a cube number)

I cannot understand how the rest of the clue works.

(Other definitions for eight that I've seen before include "Number that figures in ice-skating?" , "Two cubed" , "Number in a Boat Race crew" , "No. of stones in cwt." , "A number, sounds like swallowed" .)

I've seen this clue in The Guardian.

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