Currency is a unit.
It is a unit in the system of measurement of value. Just like an inch is a unit in the system of measurement for length.
Money is nothing like "a unit in the system of measurement for length": it measures the exchange value of whichever it prices, rather than any of its objective properties - exchange value is neither objective nor constant.
Right but we have to measure subjective entities against objective ones. Like the subjective unit of a byte is equal to a certain number of charged particles.
We cant measure opinions against opinions we have to measure opinions against facts. If we want accurate measurement.
That is what we have been doing for the last 40+ years measuring an opinion against an opinion. We have been measuring length with an inch that changes size. It is like when we measure length with a human foot.