apple watch workout is way off on calories

As far as I can tell the super-low values are either 1/2 or 1/3 the actual value. Most likely this is related to the Nyquist-Shannon Sampling Theorem (google that - fun stuff) and under-sampling the skin perfusion information which is used to determine when a heart beat has happened. Every now and again the heart rate may even show up as double, which is loads of fun -- my maximum reported heart rate is 208, and at age 54 I suspect I'd be dead if that were accurate.

If you navigate your Watch to the "Heart Rate" screen and just leave it there during a workout (it's the last screen, all the way to the right), you should see (whenever the screen is displaying data) the current / most recently measured heart rate. You can also navigate to the heart rate using "Glances", but this mostly happens during high intensity workouts. From time to time, instead of seeing a "beating heart" you'll see a heart-shaped icon that is partially grayed-out and "Measuring". That seems to happen when the Watch loses track of your heart rate and that seems to be when these 1/2-off reading happen. I do HIIT most of the time (... when I'm not walking or running to make up my "Move" goal ...) and when I shift from "low" to "high" is when the Watch loses it's mind and thinks I'm in a coma. Or dead.

Some of these errors can be fixed by wearing the watch as snug as you can stand during workouts. Sadly, that causes the rubber band to stretch, and as luck would have it I've just about stretched my current band to where I need a new one.

I Have noticed that when I use the 'other' workout type that a 90 minute yoga class, a 90 minute weightlifting session and 90 minutes of sitting watching tv all report a similar level of calories burnt. Not too confident in the watch right now.

Chris -

What you've seen is normal -- if you fall asleep while watching TeeVee, it will also record a workout about the same as a weight lifting session, if you're not doing particular challenging strength training.

"Other" is intended to be a workout which is AT LEAST as intense as a "brisk walk". So, mowing the lawn and climbing up and down a ladder is probably vigorous enough for "Other". And "Pilates" is probably vigorous enough, but 30 miles of Corpse Pose, probably not so much. It's up to you to know that you're going to be putting in a lot of exertion.

That said, I'm also losing faith in "Other" as a workout. I'm adding more stretches and rests into my yoga routine and I'm no longer all that confident in the numbers.

TL;DR - Don't use "Other" unless you plan to sweat.

I Had assumed that the point of the heart rate tracking would be to estimate a calories burn based on activity level. This does not seem to be the case. My Fitbit Charge HR would report different levels of calorie burn for the 3 activity levels - the Apple Watch does not. I do agree with you that the Other category does not seem to inspire much confidence.

I have similar results. Much experience with two different chest straps and other workout tracking.. My watch (Series 2) is snug and is properly set up for my age & weight. I get between 600-700 total calories where I should be getting right at 1000. What I have found is that the heart rate monitor just using the watch itself compares very well with my old trusty chest strap - impressive. Seems the difference is somewhere in the calculations. Hopefully this can be fixed soon.

I had this problem to, I solved it by adding my height and weight in the health app.