Primarily, a Piezometer is used to measure:

Piezometer: 

• It is a simple form of manometer.
• A device that is used to measure liquid pressure in a system by measuring the height to which a column of the liquid rises against gravity or a device that measures the pressure (more precisely, the piezometric head) of groundwater at a specific point is called a piezometer.
• One end of the piezometer is connected to the point where the pressure is to be measured and the other end is open to the atmosphere.
• It can’t be used when large pressures in the lighter liquid are to be measured.
• Piezometer is used to measure Pressure in pipe channels etc. at a point.
• It can be used to measure the positive gauge pressure of a liquid
• It can be used to measure medium or low pressure only. 
• It can't measure the pressure difference between two points.
• It can be used to measure the pressure of a moving liquid

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