I usually wear a chest strap when training whether in the gym or out on my bike. On the odd occasion I forget I rely on the watch HR sensor and I've noticed the last few sessions it's been very inaccurate. It's reads extremely low, when I can feel my heart trying to come out of my chest it'll be reading less than 100. I find this really frustrating as like to make sure I keep decent and accurate data. I've adjusted position on my wrist, how tight the strap is and switched wrists and it makes no difference.
When not training and when asleep accuracy seems to be bang on.
Any idea's what's going on? I really don't want to have to return the watch and lose all the data...
