Heart rate variability is the small, constant variation in the gap between your heartbeats. It is one of the clearest windows into how much recovery capacity your nervous system has today -- and you can read it with a phone camera.
At 60 beats per minute your heart does not beat exactly once every 1000 milliseconds. That variation is the visible result of two systems arguing in real time: the sympathetic branch pushing the rate up, the parasympathetic branch pulling it back down. RMSSD measures beat-to-beat change (the standard for short daily readings); SDNN measures overall spread across a window (more common in 24-hour analysis). Quantum Khor never mixes their reference ranges.
Typical resting RMSSD runs roughly 35-90 ms in the 20s down to 15-40 ms at 70+, consistent with the normative HRV literature (Umetani et al. 1998; Nunan et al. 2010). These are orientation, not targets -- individual variation inside each band is very large.
Raises it: a full night's sleep, slow breathing (~6 breaths/min), consistent easy aerobic training. Lowers it: alcohol, a hard training session in the last day or two, illness or stress load building up.
A phone camera can capture the same pulse signal optically -- each heartbeat changes how much light the skin absorbs. Quantum Khor's scan takes 20 to 27 seconds, cross-checks three independent extraction methods, and returns RMSSD and SDNN alongside pulse.
There is no universal good number -- two healthy adults of the same age can differ by a factor of three. What is meaningful is your own trend against your own baseline, measured the same way at the same time of day.
Quantum Khor is a wellness companion, not a medical device. It does not diagnose, treat or prevent any condition.