What are you using as your known good reference?
Garmin definitely calculates calories differently (I believe heart rate is used in the calculation) and the figure includes BMR calories as well but I have yet to see anyone to show it's wrong, just different
CW
It's high that's for sure, by about 300-500 calories per day on average for me.
I've extensively compared against my fitbit and other online calculators (over a many month baseline). As well i've tracked my weight and calorie intake for years and know that i maintain weight at about 1800-2000 calories per day.
If i turn off the all-day HRM then the number is much more reasonable from steps alone. As it is, i turn the HRM on for sleep (for RHR) and activities only. Suits me fine.
Is really crazy that we purchase one watch with HRM and we need to put this off to improve the watch measure activity. If Garmin can not do this in the good way is better for them and us to stop the production of this products.
I come back to my previous Polar V800. 400 euros trashed.
Overall my 735XT is a pretty impressive piece of hardware. It's not perfect, and i've had my issues. I love mine and would highly recommend it.
What periods did you think you got the activity calories?
"Getting ready" and "driving" may well account for some...
But the "interesting" stat is how many you get during the long "Sit". And you are not allowed to get up at all ?