On Sraffa's Standard commodity

The necessity of expressing the relative price of a commodityin terms of another commodity makes it impossible to distinguishthat part of any change that can be ascribed to the characteristicsof the commodity itself from the part of that change that isto be ascribed to the characteristics of the commodity of reference,i.e., the numéraire. Ricardo (1817) was the first topoint out this problem and the need to find an ‘invariablemeasure of value’, but he was not able to solve the problem.In 1960, Sraffa suggested using a bundle of commodities, thathe called ‘Standard commodity’, to accomplish thisfunction, claiming that it was a standard of value invariantwith respect to changes in the distribution of income. But inSraffa's book there is no explicit proof of this claim. Thisgave rise to many misunderstandings about the Standard commodityand its role as invariable measure of value. This paper proposesa proper definition of an ‘invariable measure of value’,and then proves that the Sraffa ‘Standard commodity’does fulfil the requirements of this definition.