The below diagram demonstrates how all the variables are determined in classical model:
Figure: Determination of all the variables in the classical model
a) Start at the top right. Here we determine real wage W/P and L.
b) Follow L down to the point on production function in middle to the right. Here you can find real GDP.
c) Follow GDP to left to the graph of the left in middle. This graph contains a single 45-degree line. All points on a 45-degree line have the same x, y coordinates. Such graph is used to transform a variable from y axis to the x axis.
d) Follow Y up to top left graph. In this graph you find aggregate supply that is independent of P and aggregate demand that is just the quantity theory of money. From this graph, you get up P.
e) If you multiply P from upper left-hand chart, by W/P from upper right-hand chart, you would get nominal wage W.
f) Follow Y from middle left graph down to bottom left graph. Here is S (r) and I (r) and a determination of real r and I in the balance. In C + + NX + G = Y, and because NX and G is exogenous, we can calculate C.