This demonstration Manometer from IEC is a high quality instrument designed to demonstrate the fundamentals of any manometer.
This unit can be used for measuring very small pressures (perhaps the pressure of natural gas) and for the demonstration of how such low pressures are measured in mm of water height.

It is constructed inside a strong alloy housing. It is complete with wall hanging ring and a mouth blow tube for pressurising one leg of the 'U' tube. The user may fill the 'U' tube with coloured water (water with a food dye) so that the water level is more easily seen.