Automatically Calculating FTP
Before the device can calculate your functional threshold power (FTP), you must have a paired power meter and heart rate monitor (Pairing Your Wireless Sensors).
NOTE:
The estimate may seem inaccurate at first. The device requires a few rides to learn about your cycling performance.
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Select
> My Stats > Power > FTP > 
> Auto Detect FTP.
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Select
> My Stats > Power > FTP.
Your FTP appears as a value measured in watts per kilogram, your power output in watts, and a position on the color gauge.