I go through a basic manometer problem discussing various pressure terms and hydrostatic pressure in this video in the process of solving for an unknown fluid density.

Problem description: The manometer shown is filled with water and with oil of unknown density and API gravity. The left side of the manometer is sealed and has pressure (P = 111,125 Pa) while the right side is open to the atmosphere. Determine the density of the oil and use the table provided to identify the API gravity of the oil.