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Old 03-11-09, 10:55 AM
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Location: Vancouver, BC
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Here's a quote from a Keiser Rep on how they calculate power taken from another forum (

First and foremost the M3 is not a ergometer nor is it priced like one. Power is an estimate. The price and our maximum usage (group exercise) dictate that it is not for testing and it cannot be calibrated. Though we do have some people that have used it with an IMET test when a bike is more preferential than a treadmill. One thing not mentioned below is magnet strength, they are consistent and do not weaken over the life of the bike.
To answer the question:

Watts are calculated from the gear setting. A potentiometer is attached to the magnet holder (the round cone shaped disc at the end of the shifter cable). As the shifter is moved, the cable rotates the magnet holder. A potentiometer is rotated by the rotation of the magnet holder, thus feeding information to the computer on the position of the magnet holder. The rotation of the potentiometer is broken down into 24 gear settings. A dynamometer was used to test and develop a table of wattage at various gear settings and speeds. The speed of the crank is determined by a magnet attached to the large pulley on the right crank arm and a magnetic switch attached to the circuit board in the magnet holder assembly. Each time the magnet on the pulley passes by the magnetic switch, a signal is sent to the computer to compute the RPM's of the crank arm. Power equals force times velocity. The force is determined by the magnet position and the speed by the crank speed. The lookup table is programmed into the computer and the computer simply looks at the gear setting and speed and goes to the lookup table to find and display the Watts for those two settings.
Darrin Pelkey
VP Sales & Marketing at Keiser
The Power in Human Performance"
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