Daily Activity Calories Showing as 0

If you want accurate HR (and therefore calories burn estimates) you should open the Strength Training app and record the whole activity. The OHR sensor polls more frequently in activity mode than in 24/7 mode. Peek under the watch if you like, and see the difference for yourself if you like - strobing LED's for 24/7 monitoring v solid LED's for activity recording.

This is particularly important for an activity like strength training where the wrist flexing inherent in the activity makes it harder to record accurate HR.

So that means that the watch never accurately calculates calories burned unless it's specifically logged in as an activity? Is there a way to force the OHR to poll more frequently, even if it's to the detriment of the battery?

I.e. if I'm out walking around the shops, or cleaning the garage or out mowing, I'll be burning more calories than I would be if I was sitting down watching TV, but it sounds like the Garmin's not going to show the difference?

My comments were in the specific case of strength training, which you pointed out in your original post. And specifically because this activity involves a lot of wrist flexing which can negatively impact accuracy.

Ok well in that case it’s my fault for not making it clear. Today was just an example to show that I know for sure it wasn’t working as intended. 

it has occurred before when doing non weigh-lifting exercise and I’ve forgotten to log it as an activity. 

ok so I did it again today on purpose - I was doing Leg Extensions so nothing to do with the wrist. I purposefully did a full set of 4 x 8, confirmed that my heart rate was spiking, but the watch still did not calculate any calories burnt. Here is what's shown in Cronometer:

The 68 minutes is a combination of the leg extensions, and packing away equipment/weights at the gym post-exercise, the calorie count is STILL 0.

And here is a second picture of the HR to show that it was elevated so the question still remains of why is it not counting those calories burnt?

Just record it as an activity. Is pressing the Start button really so hard?

Sure, but it doesn't really solve the initial question though - why is my Garmin watch not calculating calories burnt outside of activities logged?

Like I initially said, if I'm out walking around the shops, or cleaning the garage or out mowing, I'll be burning more calories than I would be if I was sitting down watching TV. Why aren't these logged accordingly?

You burn baseline calories just being alive based on heart rate, weight and other particulars.

Calories burned during activities (which must be started/stopped and saved to be recorded) are burnt at a different rate particular to the activity, the amount of work being done (key factor) based on the activity type, heart rate and other particulars. Typically for aerobic exercise the burn rate of calories is more than just general non activity related heart rate

So if I'm understanding you correctly, your first part is referencing RMR, which, to confirm we think the same, is simply the number of calories required to keep your body functioning at rest, or Resting Metabolic Rate. BMR and RMR are slightly different, but are often used interchangeably.

The second part of what you're saying is essentially the gap between your RMR/BMR, that will include any daily activities that may be slightly strenuous or are extended over a period of time, but not logged as a specific activity like Strength or Running, are not counted at all?

So for example, my BMR is 1,844. If I then go and do yard work for 3 hours, my caloric needs must be higher than 1,844, but you're saying that that's not counted because it's not logged as an activity?