Calorie counters are used in nearly all aerobic equipments, from treadmills to elliptical trainers. Infact there are even calorie counter that give you the calories you burn when you jog. Unfortunately these gadgets are rarely trustworthy. And if you are not careful they can be a source of frustration.
Exercising to lose weight as it is for most people is already difficult. Few have a natural motivation to keep fit. The last thing you want is a gadget that will give you false hope.
Studies show that most calories counters will over shoot your calorie expenditure by as much as 30%. With many individuals posting calorie burns of above 400 calories per session, it means that an extra 120 calories were falsely calibrated as burnt. This can translate to a deception that you have burnt up to one pound of fat in a month just by using your elliptical trainer.
Obliviously if you are using sound tracking methods like body fat percentage, you will notice the inconsistencies. But for those stuck with the bathroom scale, a more ineffective method of tracking your weight loss, the numbers will just never add up. Your counter will be telling you, "You are losing" while the bathroom scale looks like it is stuck on the same numbers since you started losing weight 6 months ago.
It is important to know that all commercial calorie counters estimate amount of calorie used in a particular activity.
The better ones require you to enter your weight, height, sex and age to better approximate the amount of calories burnt. In particular treadmills are known to be more representative of actual calories burnt. They have been around longer and their formula and calibrations are more established. On the other hand elliptical trainers and stair climbing machines are not that accurate.
Since in exercising for weight loss you are looking to burn fat, estimating how much fat is burnt is really complicated. This adds to the complexity in using calorie counter to determine amount of fat burnt in an exercise routine.
To be able to accurately determine the amount of calories expended from body fat you need to take into consideration the amount of oxygen breathed during the activity. Fat burning to produce energy is only possible in the presence of oxygen.
Machines approximate this by notifying you of a "fat burning" zone where it is approximated most of the energy for the activity is being supplied from body fat.
In reality, you use about 160-200 calories per session; above your regular calorie use (Resting Metabolic Rate). What most machines do is they show the total approximate calorie burnt including RMR, not to mention the inherent 30% error.
This does not mean you do not track your calories though, just adjust them appropriately.