When we learn keynes, we are taught the formula for AD and AS. How is it applied in real life? Do you know that there are actually indicators that track these changes and track the economy via C I G X-M? Have a look at the charts below that depicts the health of the US economy.

Aggregate Demand
NYSE: XLY, the SPDR Select Sector Consumer Discretionary. This chart measures the consumption pattern in the US economy which is something like the AD of the economy.
finviz dynamic chart for  XLY

Aggregate Supply
Basic Materials (NYSE: XLB), Industrials (NYSE: XLI) and Financial Sectors (NYSE: XLF) can be regarded as the Supply Side AS. As a process chain, XLB (Basic materials) will be input into XLI (industrial) part of the chain, and XLF (finance) will supply its input into XLB and XLI Sectors. From XLI sector, goods are produced which will then fed into the growth of services sector.
finviz dynamic chart for  XLB
finviz dynamic chart for  XLI
finviz dynamic chart for  XLF

Observe the shifts between AD and AS and what do you see?
Now you have to power to predict the health of the US economy.