That's why I kinda doubt what No 1 said about Fed is a bill printing machine. It's said bond is used to pay debt and government activities. If Fed can print bills without restriction, why bother to issue bond, which leads to more debt? You can simply print more to eliminate debt. Another issue is inflation, more money in the market means more higher inflation. The current situation is complicated by foreign countries holding a large amount of US bills, which could reduce inflation risk. But still, FED has to use some kind of measures to decide how much it can print without hurting the economy, my question is: what are the gauges they are using to determine how much they can print?