Stationary bike calories Could somebody give me an idea of how to figure out the number of calories I'm burning on a stationary bike?

The bike I'm using is a cheap Pro Fitness magnetic bike from Argos (http://www.argos.co.uk/static/Product/partNumber/9237386.htm), and it comes with a digital readout of speed, distance, pulse, calories, etc. but the calories stay the same no matter what setting I ride on.

In other words, if I do 45 minutes at 30 kph on setting 1 (extremely easy), the calorie readout will be the same as if I do 45 minutes at 30 kph on setting 8 (around 200!). Obviously this cannot be true. 

I've been using this site (http://prod.bicycling.com/training-nutrition/training-fitness/cycling-calories-burned-calculator) to get an estimation of my calories, and the calculator says I will burn about 750 calories for a 45 minute ride at 30kph, but the calculator is for bicycles and not stationary bikes. 

Are there any guidelines or info for stationary bikes only?
Since you say you have a heart rate display, you can use one of the various online calculators to convert heart rate to calories. 

Such calculators can only give you an approximate answer, but they will be better than nothing. And they're free. 

Be careful not to overheat using a stationary bike.