HRV stands for Heart Rate Variability.
Itโs a physiological measure of the tiny differences in time between each heartbeat โ also called R-R intervals (the time between successive R-waves on an ECG).
Without any tech at all
You canโt really measure HRV by hand, because it requires millisecond-level timing between beats. At most, you can take your resting pulse manually (count beats per minute), but that gives only heart rate โ not variability.
Seems like an "edge" metric at most.