On Sraffa's Standard commodity: is its price invariant with respect to changes in income distribution?

In his 1960 book, Sraffa suggested using a composite commodity,which he called the ‘Standard commodity’, to solveRicardo's search for an invariable measure of value, i.e., astandard capable of isolating the price movements of any othercommodity induced by changes in income distribution. The absencein Sraffa's book of an explicit proof of the invariance propertyof this standard gave rise to many misunderstandings about itsmeaning and its role as an invariable measure of value. In orderto clear up these questions, Bellino (On Sraffa's Standard commodity,Cambridge Journal of Economics, vol. 28, 121–32, 2004)has proposed a ‘proper’ definition of an ‘invariablemeasure of value’, showing that Sraffa's Standard commoditydoes fulfil the requirements of this definition. He claims thatthe fulfilment of this property (but not the constancy of its‘nominal’ price) qualifies the Standard commodityas an invariable measure of value. In this paper, a proof ofthe invariance of the price of the Standard commodity with respectto changes in income distribution is given, and the equivalenceof this property with Bellino's definition of invariance isshown.