In a liquid, when we use P=hρg, how do we take the h? I always thought that we take it from the bottom of the liquid but in a question, they showed that you can take it from the top so I'm pretty confused about this. Here is an example: http://postimage.org/image/oki3fq131/full/ [Broken] So from this I'm pretty confused about what direction my pressure will act on. Is it upwards or downwards? Because in this example, i took the pressure of the liquid to act downwards: http://postimage.org/image/bbf5ow2mj/full/ [Broken] so i'm really confused about the direction of pressure in the liquid. Since the pressure can exert a upwards force then aren't my assumptions wrong in the second image? Can someone clear this up for me? Thanks for the help!