@classmethod
def __cnc(cls, calib, we_c):
    """
        Compute cnc from weC
        """
    if we_c is None:
        return None
    offset_v = calib.pid_elc_mv / 1000.0
    response_c = we_c - offset_v
    cnc = response_c / calib.pid_sens_mv
    return cnc
