"You missed this?: "Each device scored one of the three pockets in the back of my club jersey. I couldn't turn them on and off simultaneously, but started and stopped each within seconds of the others." --- JeffyPoooh
You're right, I did miss that. But it's still only one run per device, so whilst my off-the-top-of-my-head suggestions for variance were wrong, I think my complaint about the test method still stands. Several runs with the same three devices are needed to determine what the intrinsic variability of each device is before meaningful comparisons can be made between them. Otherwise you end up with the "Which? effect" where, because one particular washing machine, vacuum cleaner etc. outlasted another, they mistakenly think they can form judgements about longevity of each model.