A hydraulic weighing scale
Stand in the middle of the weighing platform. Look at the level of the liquid in the tube. The height of the liquid column should correspond to your weight measured in kilograms.
How it works
The tube filled with liquid is connected to the platform, you are standing on. By pushing the platform down, accordingly to Pascal’s law, you increase the pressure inside the whole tube. This pressure called hydrostatic pressure, depends on fluid density, gravitational acceleration, and the height of the liquid column. Neither the density nor the gravitational acceleration change during the experiment, so the only result of the pressure increasing is the liquid level going up.
A French scientist, Blaise Pascal, performed an experiment in which he put a long vertical tube into a leak-proof wooden barrel filled with water. A small amount of water poured into a tube made the barrel burst. The experiment proved that the pressure inside a container depends directly on liquid column height rather than its weight.