Great article Sarah! There are so many people who think staying in the stupid "fat burning zone" helps them burn the most fat. It drives me bananas!
In my humble opinion, cardio which involves carrying your own body weight usually burns more calories than a machine which supports your body weight ie. jogging will burn more than cycling but
this greatly depends at what intensity you're working at. You may burn more in a high intensity spin class than jogging slowly on a treadmill for the same amount of time.
Also, the calorie info on machines can vary greatly and usually isnt completely accurate. The ones where you can input your info are probably better because a 50kg person would burn way less than a 80kg person.
A better way to gauge your activity is to use the perceived exertion scale whereby working out at a 7 or 8 out of 10 is high intensity.
Because on different days you will find the same workout harder or easier depending on sleep, if you've eaten breakfast, TTOM, fitness level increase/decrease etc etc.
Hang on, I think I have it here somewhere *rummages through messy desk*
Level 1: I'm watching TV and eating bon bons
Level 2: I'm comfortable and could maintain this pace all day long
Level 3: I'm still comfortable, but am breathing a bit harder
Level 4: I'm sweating a little, but feel good and can carry on a conversation effortlessly
Level 5: I'm just above comfortable, am sweating more and can still talk easily
Level 6: I can still talk, but am slightly breathless
Level 7: I can still talk, but I don't really want to. I'm sweating like a pig
Level 8: I can grunt in response to your questions and can only keep this pace for a short time period
Level 9: I am probably going to die
Level 10: I am dead
I wouldnt worry too much about what the machines say but more about whether I think I gave it my all. Sometimes I find exactly the same workout feels much harder than a previous time. There's usually a reason for it though.
Anyway, hope that helps.