Pressure potential is a component in water potential, which is is the potential energy of a unit of water volume in given conditions relative to the same volume of pure water. Pressure potential is a measurement of the tendency of water to move from one area to another as a result of mechanical pressure. If you know the depth below the free water table that you are measuring, calculating the pressure potential can be done with a calculator.
Measure the depth in meters below the top of the free water table for the point at which you are attempting to calculate the pressure potential with your meter stick.
Divide the depth in meters measured in Step 1 by 10 and add one to the result to calculate the amount of atmospheres of pressure present at the depth.
Multiply your result from Step 2 by the difference in depth measured in Step 1 to get the pressure potential per unit volume of the water at the depth you are measuring.