Resting heart rate

How many times your heart beats per minute when you are fully at rest -- ideally measured before you get out of bed, not after walking to the machine.

It falls as cardiovascular fitness improves and rises with illness, alcohol, poor sleep and stress, which makes it one of the few numbers here that answers within days rather than months.

The 60 to 100 band is the clinical definition, not a fitness target: a well-trained person sitting in the 40s or 50s is normal and will show here as below range. Only comparable readings belong on one line, so log a morning watch reading and a clinic reading under different sources and let the chart draw them separately.

Worth mentioning a resting rate that has climbed over weeks, or one that comes with palpitations or breathlessness.