Q. Can you explain Pneumatic gauges?

Pneumatic gauges permit reading or recording water level at some distance from the river, say up to about 305 m. In a diaphragm type gauge, water presses against metalIic diaphragm fixed to a metal air bell. Air inside the bell changes its pressure with the variation in depth of water column above the diaphragm the air belI is connected by tubing to a dial indicator which can be located in a cabin at a safe distance from the bank. In a bubble type pneumatic gauge, the bell is provided with a slot. The air pressure is read by manometer and converted to depth of water and thus the water level is obtained. Electrical long distance gauges are also available of different forms