Automatic calculation of maximum heart rate

I’m not sure if it’s accurate at all, it kept pushing my Max HR higher and higher with every workout… well above what I believe it should be so I disabled it.

Based on rule of thumb calculations (220 - {your age}) I should be around 185bpm the watch was eventually calculating 210 bpm for me which I don’t think I’ve even got remotely close to.

My highest activity in recently was during a ramp test at 181 bpm about 2 months ago. Which makes me think what I’ve manually entered is about right.

220-age is a method for the average population max HR but it can vary a lot, and it's not accurate at all for one individual value. I would really not recommend using it (I am 48 yo, and my max HR is around 187 bpm...). And actually max HR is not so hard to test if you are exercising regularly. Find a hilly road (ideally between 8 and 10%) that you can run for at least one minute, and after a good warm up (or even better at the end of your easy run) go for it and try to reach maximum effort. Your HR when you reach the top (or after one minute) should be quite close to your max HR.

Doesn't change the fact that max hr detection is broken and also lactate treshold detection. 

Before I sold my Fenix 8 my max hr was detected between 160-200bpm and lactate treshold 181bpm. I had to disable both. It was suggesting base runs at 170bpm (my actual max hr is 194bpm). 

For some reason my Coros is detecting my max hr 100% accurately and lactate treshold at 169bpm. At 30% of the price of Fenix 8. 

It came up with a value of 190 the other day from a relatively short run of relatively low intensity. I'd hit 192 on the finish line of a 5k a few days earlier, so on the one hand it wasn't far out at all, on the other hand, it seemed to be ignoring what looked like a perfectly good recent value.
As an estimate, though, it was way way better than 220 minus age.