How does the laboratory control the flow of N2 in the N gas cylinder?

Nitrogen, go to the market to buy a nitrogen meter, tens of dollars. Install it. There are two indicator lights on it. One is to display the pressure of the nitrogen cylinder, and the maximum range seems to be 25MPa. Another reading is that nitrogen actually flows out of the meter. According to the reading of the small instrument, you can control the flow of N2 by slowly turning the knob of the nitrogen meter! ! !