@Olaf-Gottschalk Yes, I’ve had that with both the Vertical and now with my Ocean. Is rare But definitely happened… I always noticed that by chance because I usually wear a belt

@zhang965 no I haven’t yet… I think this is a problem with the software and I hope for a fundamental update so that the Vertical’s software finally runs stably. Maybe the memory is full or something similar… ? Even if Suunto were to offer me the exchange of a new watch, I don’t think it would work more stably… I hope for an update soon…I was just interested if other users had observed something similar. That’s only noticeable if you want to do sports and the watch doesn’t find a heart rate. I usually use a heart rate belt and it has always worked.

@markeczzz interesting observation.
Do you have an idea what could be different for the watch when you are climbing?
The watch is basically trying detect the capillary blood flow.
Bad measurements could come from a too tight strap (blood flow interrupted), a to loose strap (watch shaking and thus variation in the optical path), cold temperatures (capillaries have less blood), using poles (introducing rythmic vibrations of the watch), tatoos, etc.

What parameter (within arm/watch) are changing when you climb? Maybe you can observe anything?