You only vary a sec check question when by repeating it you would create an impasse.

Example: "Have you stolen anything?"

"Yes, an apple."

"Good. Have you stolen anything?"

"No."

"Good. (Look at meter.)

Have you stolen anything?"

"No." (Meter reacts.)

Now vary the question.

And always end by making sure the original question "Have you stolen anything?" is nul.

This all comes under the heading of getting one auditing question answered before you ask a second.

If you create an impasse you will pile up missed withholds, throw ruds out and really mess it up. Therefore, until you do find out what the answer was on a sec check question, you do not repeat the question — only variations (except to test for nul after getting a withhold) until the meter nuls on the first question.