My favorite calibration tools have been one where there was a numerical answer and you had to express a 50% confidence interval, or 90% confidence interval.
Like, a question would be how many stairs are there in the Statue of Liberty? And my 50% interval would be 400-1000, and my 90% interval would be 200-5000.
Looking up the answer it was 354, and I would mark my 50% as wrong and my 90% as right.
If I had to guess, Voldemort did something so Snape understands how Dumbledore manipulated him. Considering how pissed off Voldemort was that Dumbledore would do that, it seems likely that he would find a way to change that now that Dumbledore is gone.