Accuracy

The Wattbike is certainly an exceptional ergometer, and the excellent repeatability of testing is ideal for training facilities where athletes are tested regularly for fitness program effectiveness.

Tom Stanef, Senior Technical Officer, South Australian Institute of Sport, 7th April 2010

 
The Wattbike ergometer has been designed to measure a maximum power of 3760 Watts, independent of the air brake, magnetic brake settings and environmental conditions.
Wattbike is designed with a high end range, so that it can measure short sprints, in particular the first kick on the pedal when the flywheel is accelerated from zero.
As with other ergometers it is not possible to have the same accuracy over the full range. The Wattbike has a higher error under 100 Watts than above 100 W.
The mean accuracy of the Wattbike is typically within 2% (-0.42% +/- 1.21%) with retest variance typically better than 1% (0.42% +/- 0.46%) - South Australian Institute of Sport 31/03/2010.
Split down into intermediate ranges the Wattbike accuracy is typically:
 
Range Error
<100 Watts up to 6 % or 6 Watts
100 - 200 Watts within 2%
200-500 Watts within 1.5%
>500 Watts within 1 %
Over the full range within 2 %

 

Ergometer accuracy and Terminology

Specifications for a calibrated ergometer can be written in different ways. When comparing the accuracy of ergometers it is important to understand the differences to avoid misinterpretation or being mislead. This is true for many of the parameters measured by ergometers including statements about accuracy.
Understanding errors and accuracy is important when selecting an ergometer for a specific application or when trying to evaluate its performance
In any measurement system there will be some error. Even the most accurate test meter still has some error.

 

Absolute error

Absolute error is the difference between the ''real value'' and the ergometer reading, in engineering units.
If the ''real value'' is 50 Watts and the ergometer reads 47 Watts the absolute error is 3 Watts.
Using the absolute errorout of context may not represent ergometer accuracy and may mislead.  A 3 Watts error on 300 Watts is 1%, but is 6% on 50 Watts.

 

Relative error

Relative error represents how the absolute error relates to the ''real value''.
If for example the ''real value'' is measured at 300 Watts and the ergometer reads 297 Watts. The absolute error is 3 Watts.
The relative error is 3 Watts divided by 300 Watt multiplied by 100 = 1% (of 300 Watt). The accuracy is 99%.