TLDR; easyish ride, HR much higher than it felt.
I don’t have a PM on my winter bike so when I can be bothered I stick on a HRM. I haven’t used this particular one in a while (CooSpoo) but seem to remember it being OK. Had to put a new battery in as it was dead.
Anyway went for a solo Sunday ride. Kept it fairly easy but every time I looked at the HRM it was way higher than I expected. On a few mellow hills I was touching 170bpm - felt slightly uncomfortable, but this would usually have me grimacing big time.
The overall average for the ride was 155bpm, that’s what I’d expect for a full on effort for 50 miles. 130-140bpm is what I’d expect. Point is it felt fairly easy.
I don’t really get how a HRM could be wrong though - I mean it’s a pretty simple bit of kit. The graph doesn’t look obviously crazy either.