This Pascal's Apparatus, developed to demonstrate principle of Pascal, consists of a machined body incorporating a horizontal flexible diaphragm to which one of three alternative glass vessels can be fitted. The diameter at the base of each vessel is common but the shape of each vessel varies; one parallel sided, one conical and one tapering inwards.
The diaphragm, located at the base of the vessel, conveys the force from the water inside the vessel to a lever arm with a sliding counterweight. A spirit level indicates when the lever arm is horizontal and therefore balancing the force / pressure at the base of the vessel. The force on the diaphragm depends on the depth of water above the diaphragm and the area of the diaphragm that is constant for all three vessels.
Lever arm with sliding weight and spirit level measures force at the base of the vessel