During calibration, I count from 1 to 10 in English, then French, Spanish, Russian and German. That keeps my mind active. I think switching from language to language helps keep things active.
I fear that doing any math during calibration would just give me a bad attitude for the meditation session.
When I first started using Muse, I tried to develop calmness during calibration. But that doesn’t make sense. You don’t want to skew the results by setting the bar too high. It does make sense that you’d want the calibration to be for an active mind, the base line from which you want to improve during the meditation session.