https://www.linkedin.com/pulse/liquid-volume-horizontally-mounted-cylindrical-tank-thomas-scharmann
Calculate the fraction of the circle's area that is the circle's segment ACE
Taking Equation R and dividing it by Equation A provides the fraction of the tank's volume that contains liquid.
Calculate the volume in the tank
Multiplying Equation S by the total volume capacity of the tank provides the liquid volume of the tank.
Equation T is the formula to be used in code. Replace h with the level transmitter's output, not forgetting to account for units, and the output will be the liquid volume.