I've been solving fluid mechanics problems and i encountered two problems that made no sense to me. Both problems that ask about the force done by water on a VERTICAL wall under the level of water. One problem was solved by taking the integral of the gauge pressure and multiplying it by the area while the other was solved by also taking the integral of the gauge pressure and multiplying it by the area of the wall but after finding this value, the force due to atmospheric pressure was added. What happened There?? why two similar cases are solved in different meanings, anyone got any idea?