Always useless, the tech just isn't designed to be that accurate.
What do you mean about the tech Brad? Certainly my wrist HR readings are usually inaccurate too. Do you mean that Garmin are selling us all a device with underlying tech known to be not suitable for the purpose?
Oddly on this occasion I had HRM strap. Think it might need a wash!
Jon - if you read the small print, you'll see that even Garmin acknowledge that the optical wrist-based HR monitor is only designed for monitoring general trends in your HR (such as resting and sustained HR) and isn't reactive/accurate enough for tracking your HR in athletic activities. Even the best wrist-based HR monitors will never be a patch on a (clean!) HRM strap. So - yeah, no matter what their headline marketing says, there's always a get-out in the detail.
The HRM also starts to go a bit mental when the battery (of the HRM, not wath) is getting low.
As Brad says, the wrist HRM is for your daily stress score, if you want to have HR data for training, then you'll need to buy the strap.
I've wasted a lot of my time telling athletes that the wrist one is useless and they need to buy a chest one if they actually want to monitor their loads.
Sounds like I had better find my old HR strap then! Thanks both.