Discrepancy in HR data between daily and 4-week chart

Marek said:

I found other threads reporting exact same issue and it was linked to the HRM Plus strap recording some artefacts after being taken off the chest. 

Yeah, I once saw a very high fake HR reading (around 220 bpm), when I took off a chest strap after a run and rinsed it with water, while it was still connected to the watch. The way to prevent this is to make sure you close any activity before taking off your chest strap, to ensure that the chest strap is disconnected. (At this point, you should also avoid using the HR widget/glance, because opening the glance will cause the strap to reconnect.)

I think I've also heard of fake HR readings from an HR strap that's just sitting in a gym bag. So I think to be safe, you want to make sure that the strap does not connect while you're not wearing it. If you need to be 100% sure of this, you could always explicitly disable the HR strap connection in the Sensors menu, when you are not using the strap.