And that means we have to add some term to our P real to equate that to our P. Likewise, our Vreal is larger than the ideal and that's why we have to subtract some term from it, some term Y to get the ideal. And so, from experiments, scientists found out what this X and what this Y was. This X is N squared times A over V. Two this Y is N times B. Now, an is simply number of moles, and B is volume a and B are constants that depend on the gas being used. And so they're different for different gases. Now, once again, the reason we have this guy, the reason we're adding this guy to P real is because P real is smaller than P ideal.