code: def distance_centimeters_ping(self):
          
          # This mode is special; setting the mode causes the sensor to send out
          # a "ping", but the mode isn't actually changed.
          self.mode = self.MODE_US_SI_CM
          return self.value(0) * self._scale('US_DIST_CM')
docs: Measurement of the distance detected by the sensor,
          in centimeters.
  
          The sensor will take a single measurement then stop
          broadcasting.
  
          If you use this property too frequently (e.g. every
          100msec), the sensor will sometimes lock up and writing
          to the mode attribute will return an error. A delay of
          250msec between each usage seems sufficient to keep the
          sensor from locking up.