Since about 3 years I've been counting calories and let various wrist watches with 24/7 heart rate trackers (fitbit, later garmin devices) estimate energy expenditure.

So I measure energy in and out (with unknown error bars). The energy balance I get as a result predicts what my body weight should do.

My control is stepping on the scale every time before I take a shower, log, and observe trends.

Result, consistent over the last three-ish years: my measured weight does almost exactly what the calorie counting and wristwatch estimating predicts. I see absolutely no systematic error in one direction or the other (measured over weeks, that is, to do away with short term fluctuations).