How to determine the pressure at the bottom of a vessel using a ruler?

The water pressure at the bottom of the vessel can be expressed in the formula:
Р = ρ * g * h, where ρ is the density of the liquid in the vessel, g is the acceleration of gravity, h is the height of the liquid level in the vessel.
The density of the liquid in the vessel and the acceleration due to gravity are reference values. The only variable value will be the level of the liquid in the vessel. It is it that can be measured with a ruler and, substituting the resulting value into the formula, determine the pressure on the bottom of the vessel.