s are:
    #  hardware        - use the value provided by hardware
    #  software        - use the value calculated by weewx
    #  prefer_hardware - use value provide by hardware if available,
    #                      otherwise use value calculated by weewx

    pressure = prefer_hardware
    barometer = prefer_hardware
    altimeter = prefer_hardware
    windchill = prefer_hardware
    heatindex = prefer_hardware
    dewpoint = prefer_hardware
    inDewpoint = prefer_hardware
    rainRate = prefer_hard