It’s from What has Gov Done to our Money Page 17:
“Money does not “measure” prices or values; it is the common denomina-
tor for their expression. In short, prices are expressed in money; they are
not measured by it.”
It means money is not a yard stick. The price of a commodity in not some objective measure of value for that commodity. It simply reflects (or expresses)the price at which the last voluntary exchange took place.
That sounds very right. Thank you.