How accurate are calorie monitors?

I decided to experiment and see how accurate calorie monitors are.

Cardio machines such as bikes and treadmills use standard formulas to figure out how many calories are being burned.
However, important factors aren’t taken into consideration: weight (unless the machine does have the capability to insert that info), body fat percentage and level of fitness.
A person with a lower body fat percentage and higher muscle mass will burn more calories than a person with high body fat percentage and lower muscle mass even running the same pace for the same time.
So these calculators should be used for general idea of how many calories you’re burning during your workout.
Some studies and reports claim that most machines overestimate calories expended by 15-25%.
As you’ll see from comparing my findings, that wasn’t the case (unless the Bowflex is way off as well).

I have a calorie counter built in on my Schwinn 120 Upright Biodyne bicycle display-the one in the Biodyne does allow me to input my age, height and weight. However, it can’t distinguish my body fat percentage or other vital information to calculate the calories perfectly. But aside from that, the fact that I can input my height, age, weight is a plus over many other machines.
I also wore the BowFlex monitor on my wrist as well.
I’m using both to compare the same workout–a 90 minute ride on the Biodyne.

I rode the bike for 90 minutes at an average of 17.06 mph, going a total of 25.6 miles overall.
On the BowFlex it shows 1 hour 30 minutes time and 756 calories(higher than the bike’s calorie monitor, which reports say some cardio equipment-ellipticals, bikes, treadmills-over estimate–so if that were the case then what’s the deal with the Bowflex being higher than the bike?)
There was no information input into the Bowflex, simply strap it on my wrist and start pedaling.
The reviews and info I’ve found on the Bowflex is that it’s pretty accurate.

you can click the image to see it full size in new window to read display better

Sorry in the pic of the bike display I had to set it for 91 minutes so I could stop and take a pic of the display before all the time was up, because as soon as your time is up the full display turns into a scrolling display and I wanted all the info visible in one pic. but it doesnt show the time, but it was for 90 minutes.
As you can see, there’s the mileage of 25.6 miles and the calories burned: 704 (52 less than the Bowflex showed)

Either way, I’m using both these as a rough idea on how many calories I burn.
Next I’ll use Bowflex while running but this was ideal since I had the ability to use 2 calorie monitors during the same workout to compare data.

I’d love to demo the Body Media — a system that gives you highly accurate information on activity, calories and sleep patterns or the BodyBugg — a monitor system that makes it easy to manage the calories you consume and burn so that you can stay in control of your weight to see how they compare to the Biodyne and other methods of calculating how many calories I’m burning and other pertinent data to help me stay on point during my workouts.