In the first part of Production of Commodities by Means of Commodities, four equation systems are introduced: three are drawn up in order to solve the problem of relative prices; the last one is devised to define a suitable standard of prices. The book was published in 1960, but\u2014as we are told in the preface\u2014its \u2018central propositions\u2019 and a first version of the price equations had been originally conceived and written more than 30 years before, when the author was still in his twenties. Having access now to the Sraffa Papers, preserved in the Wren Library, we can ascertain the intellectual origin of the equations. In this paper the analytical path that led to the final draft of the price equation is followed, step by step, and the link between these equations and Sraffa's quest for an \u2018invariable standard of value\u2019 is clarified
