The control was a Polar H7 Bluetooth chest strap that has been touted to be one of the “most accurate consumer devices for measuring heart rate”, and as for going off tangent, the Microsoft Band might have a bad day at the proverbial office by being off by “as many as 13 beats” per minute.
As for the Apple Watch, how did it fare? It apparently did not hold a candle to the Microsoft Band, so you can more or less forget about it being in tandem with results from the Polar chest strap. Metz claims that the Apple Watch “gave readings as many as 77 beats per minute different from the Polar device.” All in all, both devices should not be substitutes for a medical checkup or the proper, dedicated equipment, but they do give you a general reading.