Apparatus for determining experimentally the relationship between gas volume and pressure at constant temperature (Boyle’s law). The working cylinder is made of transparent acrylic and has a moving piston, scale and manometer. Along with a valve to let in gas or release it. The movement of the piston is achieved with the help of a threaded connecting rod turned by means of a manual crank. In this way, pressure both above and below atmospheric can be generated. For safety reasons, the working cylinder is enclosed in another protective transparent acrylic cylinder. Piston dimensions are 30 x 40 mm with 2 sealing ring gaskets. Manometer diameter is 100 mm.