The invention relates to group communication services, i. The passive tag converts data stored in the memory unit into a data packet in response to first to third data request signals from a reader and transmits the data packet to the reader. This measured data is obtained using a multi-phase flow meter before a separator of the underbalanced drilling system. Alternatively, the differential optical delays are different from one another. The system device is configured to monitor a TV or video source regularly watched by a viewer and provides TV programs or videos to be in accordance with a viewer’s interest.