Gold/M2SL(Billion USD) is currently around 0.12. In 1980, it peaked around 0.45. Monthly average since 1960 is 0.11. In late 2011 it peaked around 0.18.
Gold / Global M2 would be a better metric, but I haven't analyzed that yet.
For those who are actually interested in this field, the proper way to measure this would be with a four point probe. You do need a constant current source and a high-impedence voltage meter, though.
Also, you don't need to solder wires to the sample. But if you want to measure the hall resistance of a thin film of a semiconductor, you can solder a glob of indium on to four corners of a 1 cm x 1 cm wafer, put it in a magnetic field, and then do basically the same measurement as four point probe, except not inline.
But `GET(GET(x))` doesn't make sense, in general (and if it did, then you would not expect it to be idempotent), so clearly idempotency in this context is meant to mean side-effect free. They should probably just say side-effect free, though, to avoid the confusion.
Oh, the irony.