According to the standard version ofthe labour theory of value, labourvalue of a product is defined as the social average of the amounts of labour embodied in the homogeneous products on the supposition that the scale of the production is appropriate to the social demand for the products. In case of joint products, the amount of labour directly and indirectly necessary for their production needs to be divided among individual joint products before calculating the average. In the labour division, the composition of demands for heterogeneous joint products must be considered because it will be different from the composition of the products which is fundamentally determined by the technical relations of production. The labour division among joint products, therefore; is understandable
through two logical phases. First, without any consideration for the gap between demand and production peculiar to joint products, the amount of labour necessary for production is divided equally among categories of homogeneous joint products. Second, the division of necessary labour is modified by the consideration for the gap. The labour divided into unsold products is divided again among other joint products sold in higher proportions to production because the former are the useless by-products of the latter. The amount of labour commanded by each joint product may be further deviated from the average of its embodied labour after the modification. Labour-values of joint products should include the part of deviations which reflects the reduction of the gap at the markets.