A 3 graduated (0-300) cm3 transparent cylinder has a screw type piston and is connected to a pressure gauge. The pressure inside the cylinder can be adjusted by rotating the knob connected to the piston. A gas tap allows the cylinder to communicate with the outside air to adjust the mass of air enclosed. The pressure can be directly read from a pressure 5 gauge circular dial, graduated in (0-3.4) x 105Pa. This smaller more economical version gives better and precise results for the Pressure / Volume relationship of air at constant temperature.