code: def setup_sensors(self):
          
          self._add_result = Sensor.float("add.result",
              "Last ?add result.", "", [-10000, 10000])
          self._add_result.set_value(0, Sensor.UNREACHABLE)
  
          self._time_result = Sensor.timestamp("time.result",
              "Last ?time result.", "")
          self._time_result.set_value(0, Sensor.INACTIVE)
  
          self._eval_result = Sensor.string("eval.result",
              "Last ?eval result.", "")
          self._eval_result.set_value('', Sensor.UNKNOWN)
  
          self._fruit_result = Sensor.discrete("fruit.result",
              "Last ?pick-fruit result.", "", self.FRUIT)
          self._fruit_result.set_value('apple', Sensor.ERROR)
  
          self.add_sensor(self._add_result)
          self.add_sensor(self._time_result)
          self.add_sensor(self._eval_result)
          self.add_sensor(self._fruit_result)
docs: Setup some server sensors.