I see lots of lay people answering this question but there is no reason it shouldn't be included in the normal choices since many stay at home moms do not have the option of using the stair stepper at the gym and you don't know your rate of work when you are doing steps.
Calories burned for steps per minute. You could have different rates...
100steps/minute at X minutes burned xxx calories 20 steps/minute at X minutes burned xxx calories
