AD7747 capacitance offset calibration mode

Hi All,

      I'm having a probelm on setting the zero-scale capacitance, below setences are copied from the AD7747 datasheet. Can anyone explain about this.

"One method of adjusting the offset is to connect a zero-scale
capacitance to the input and execute the capacitance offset
calibration mode. The calibration sets the midpoint of the
±8.192 pF range (that is, Output Code 0x800000) to that
zero-scale input."

Thanks

Nicky