I feel pretty good about my max HR measurement. It was derived on a track, with a chest strap, and another person holding the receiver, noting my HR every 100 meters during two 400 meter sprints (after a warmup and with a brief jog interval between 400 meter sprints). While I could probably get something even more accurate in a lab, that seems good enough for now.

And I totally understand rejecting the “formula.” I’ve seen max HRs vary greatly from the 220-age formula (or the several deviations from that formula).