> Chai-on:
>
> Yes, it needs to be a commodity so as to function as a sacle to measure
> prices. Though the spring sacle measures the weight without equivalent
> weights, it still has some reference to the real weight scale.
>
Weight is just force, so that a force measuring device like a
spring balance is suitable for its measure.
A in order to measure something one needs a technology of calculation
and some system for representing the thing to be measured within that
technology of calculation. The system of representation is adequate
so long as it is consistent with the properties of the the system
being measured. If the underlying system obeys the triangle inequality,
as value does, then we want the measurement system to do the same.
Metal money, along with all coinage is both a system of representation
and a technology of calculation. Collections of coins themselves act
as a record of how much value somebody has, and by mechanical operations
on the coins allow calculations to take place.
.