@mckao The monetary base is the amount of U.S. currency the banks have in reserves. The central bank measure it in adjusted terms. The point is the central bank drastically increased the money supply during this prolonged crisis that began in 2008 and is deceptively called a recovery. Dig deeper and since the gold component was removed by Nixon 1971 you see the banks began creating dollars in huge amounts...

If you want the mechanics of how the central bank adjusts that monetary base statistically then go to the federal reserve bank of St. Louis website.
I hope that answers your question.