Value in FIT file not viewed in GC

I have calculate one value of virtual power and after i have write it in the FIT file.

The power is regulary in FIT file, but when i upload file FIT in Garmin Connect the value is not present in the graphs of GC.

In Delegate module i have create session and createField:

powerFF = session.createField("Watt", 1, Fit.DATA_TYPE_UINT8, {:mesgType => Fit.MESG_TYPE_RECORD, :units => "watt"});

i the View module i have calculated value of power and after setData the value:

powerFF.setData(power.format("%0.0f"));

why not display the value of power in the graph of GC ?

thanks much