Visit your doctor and, invariably, the office staff will check your pulse.

For years, medicine has espoused a “normal” range for resting heart rate, also called pulse. Comparing a patient’s pulse to the normal range helps doctors identify, among other things, when the patient person is dehydrated, out of shape or under stress. But how accurate is the established range?

Smartwatches and other forms of wearable technology have made it easier to study pulse more closely than ever before. A study conducted by researchers at Scripps Research Translational Institute asked participants to wear a pulse-tracking device regularly over 35 weeks. The idea was that recording pulse over an extended time period, instead of just a brief look during a doctor visit, would give more insight.

About 92,000 people joined the study. Their heartbeat records showed an enormous range of what normal adult pulse can be, anywhere from 40 to 109 beats per minute. That’s a 79-point difference!

The study authors note that despite the great variation between people, each single person was pretty consistent in his or her own pulse. When a person’s heartbeat was notably off track, it was for a short period of time.

But small pulse variations may provide the most valuable information. A person with a quick heart rate increase over a few days may be fighting an infection. A slowly increasing pulse may mean declining cardiovascular health.

Among the participants as a whole, the authors saw a strange trend. Pulse peaked in early January, and then declined until late July. After that, pulses began increasing again. The reason for this seasonal fluctuation remains a mystery.