The problem with using resting metabolic rate as a starting point is it will be difficult to assess calories burned through all the different activities done during the day, like washing dishes and pushing a vacuum. Also, at least on my watch, calories burned outside of exercise due to normal daily activity is probably way off. So in order to include calories from normal daily activity, an estimation would have to be made for this part, which for instance, can be a percentage added over the resting metabolic weight. Many of your calculators online use this approach. I do not think there is any realistic way to do this otherwise. As a consequence, this calculated amount can be more accurate some days, and less accurate in others.

By the way, from my reasearch, the calculation of the resting metabolic rate needs to include the percentage of body fat. From what I have learned so far, this can make a significant difference in accessing the calories burned with respect to ones metabolic rate. I guessed mine to be 25%. This made a significant difference to the result. The typical online calculator places my RMR to be around 1800. However, when using a calculator that includes percentage body fat, my RMR ends up being about 1400 calories. I estimated the 25% by critically examining many of the photos available on the online. Those are the photos of actual people that display a percentage fat along with how it makes the person look.

I found one equation that determines the calories expended during exercise using a value that describes your fitness level. This is called VO2max. This would need to be included in the calories burned calculation, since the more fit someone is, the less calories they burn for the same exercise. This formula is available online. My watch includes all of this in its calculation of calories burned for an exercise. However, this does not mean it’s accurate. There are several different formulas that can be used that attempts to calculate the same result. Also I think there are still assumptions that needs to be made even when considering all of these variables that I specified above.

So calculating calories burned appears to be more complex than much of the online information leads us to believe. I think the best way to approach this is to take the amount given by a formula that perhaps includes the most relevant of these variables, and adjust it for your particular situation. For instance, it need not use VO2max since fitness changes slowly. Also if you can try to manage expending the same amount of effort in all of your walking exercises, this can further eliminate variables. Your can measure this effort by trying to keep your hear rate within a specific range. The calculation of your RMR may not need to include the percentage of body fat. This also changes slowly when not trying to shed pounds.

I think the finding of a suitable result would involve trial and error until you find a percentage adjustment that will allow you to maintain your weight. I see this is what you have been attempting to do with your watch. However, IMO the use of some kind of formula may provide a more consistent result which then you then adjust by that percentage for your situation. IMO the formulas used do not have to be very accurate. They just need to aid in providing a consistent enough result which then you can adjust.

As far as the estimation provided by your watch goes, perhaps it can provide a usable value with some adjustment. However, I think you will not know until you calculate the calories burned yourself over a period of time using some type of formula mentioned above as a gauge. As respect to my situation, I will be finding the percentage to adjust the value by that will keep me weight neutral. I am assuming it is making the calculations in an intelligent mamnner, and it is providing a consistent result.

There is a way that appears to simplify this problem to an extent by using MET values. The MET value, standing for metabolic equivalent, describes the amount of effort put into a particular activity, in relation to other activities. MET values for hundreds of activities have been compiled, and is available online. What is nice about this is that this value can be used not only for specific exercises, but also much of the daily activity itself. For instance, I think there is a MET value for washing dishes.

PS I still think 50 calories a mile is low. Many of the formulas provided online seems to validate this. However, even these formulas in the form of calculators need to be taken with a grain of salt. I guess what is more important is consistency.

IMHO YMMV