(2009? As shown in the figure, the purpose of the instrument is _ _ _ _ _, and the pressure on the rubber membrane during use can be expressed by _ _ _ _ _.

Observing the image, we can know that the name of the instrument is: U-tube pressure gauge; When the pressure acts on the rubber membrane of the U-tube manometer, the liquid levels in the two tubes will not be on the same horizontal line and there will be a height difference. The greater the pressure on the rubber membrane, the greater the height difference of the liquid levels in the U-tube manometer, so the pressure on the rubber membrane can be expressed by the height difference of the liquid levels in the two tubes.

So the answer is: measure the pressure of the liquid; Liquid level difference.