Demo: sample numbers, not anyone's real measurements.
6 October
How much load you took on today, scaled to what is normal for you. Zone minutes count for more the harder they are; steps add a little.
These bands are the same for everyone. Your own usual is the band on the dial.
Strain is not good or bad on its own. Read it against today's target.
load = zone minutes x [1, 2, 3, 4, 5] + steps / 1000 x 1.5 scale = 0.9 x your 28-day 90th percentile load strain = 100 x (1 - e^(-load / scale))
The same formula scores the web and iPhone apps, and it is covered by tests.
Past today's target of 35 to 55. Keep the rest of the day easy.