Calories Seem Inaccurate? (Watch)
With Apple Watch, I'm relying on Apple's estimates for calories. They combine the heart rate sensor and motion events, and knowledge about you from Apple Health (like age / weight / etc) to determine how much you've burnt. They've put a ton of research into those estimates, so I'm trusting them.
If the calories seem lower than expected: Make sure your Watch band is tight and you have direct skin contact so it can pick up on your heart rate.
If the calories seem higher than expected: You might actually be burning more calories than you think! A day on the groomers might not burn a ton of calories, but add some fresh snow to the mix and your legs are working a lot harder than you might realize.