i guesstimate the best i can. I usually do pretty well with the numbers that SP provides. If it is a little more or a little less, I don't really worry about it. I am not a stickler. As long as i am moving and feel great, I don't concern myself with calories burned.
Perhaps take a look over your recent results, and see how many calories per minute you typically burn. 8-10 calories per minute would be typical for someone who works out regularly, 10-12 if they were really pushing themselves hard.
How do you calculate the calories burned without a HRM? I have been so dependent on mine and now I can't find the most important part - the wrist piece. I just have no idea how to gauge how many calories I am burning.
Is the fitness tracker accurate? What do I use for an Arc Trainer (it's not listed)?
I do plan in ripping apart the house for an hour after work to see if I can find it, but in case I can't find it, I can't stop working out :(