Tap along with your heartbeat.
Two fingers on your wrist or the side of your neck. When you feel a beat, tap. I'll do the arithmetic.
four taps give a first guess; ten make it trustworthy.
finding a pulse you can feel
The wrist spot is on the thumb side, just below the crease — two fingertips, never your thumb (it has a small pulse of its own and will happily confuse you). The neck spot is in the soft groove beside your windpipe, pressed gently. Give yourself a quiet moment; a faint pulse becomes obvious once you stop hunting for it.
Then just tap this page in time with what you feel. Spacebar works too, if you're on a keyboard.
the same median, by hand
This page uses the very same idea as the camera measurement: collect the gaps between beats, sort them, and take the middle one. If you fumble a tap — everyone does — that odd gap lands at the edge of the sorted list where the median never looks. The steadiness note beside your BPM tells you how consistent your recent taps were, so a wobbly count can't masquerade as a precise one.
Tapping is also the honest fallback when camera readings fail: iPhones that won't light the flash for a webpage, laptops with no rear camera, wintry fingertips with no blood in them. People counted pulses by touch for a few thousand years before anyone owned a camera — you're in good company.