code: def startMeasurement(self, measurementId, deviceId):
          
          am, handler = self.getDataHandler(measurementId, deviceId)
          if am is not None:
              am.status = MeasurementStatus.RECORDING
              am.updateDeviceStatus(deviceId, RecordStatus.RECORDING)
              handler.start(am.idAsPath)
              return True
          else:
              return False
docs: Starts the measurement for the device.
          :param deviceId: the device that is starting.
          :param measurementId: the measurement that is started.
          :return: true if it started (i.e. device and measurement exists).