Standard deviation in tricky ads (9)

I believe the answer is:

yardstick

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

'standard' is the definition.
(I know that yardstick is a type of standard)

'deviation in tricky ads' is the wordplay.
'tricky ads' anagrams to 'YARDSTICK'.
However, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for yardstick that I've seen before include "Criterion - means of measuring" , "Standard of measurement" , "General measure for comparison" , "Ruler or tape, three feet long" , "Benchmark" .)

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