There is no difficulty, however, in choosing numbers which satisfy the requirements of the model. The numerical examples derived from Marx's jottings are cumbersome and confusing, but a clear and simple model can be constructed on the basis of the assumptions set out in chapter vii. In each department, constant capital is four times variable capital.[18] (Constant capital is the stock of raw materials which is turned over once a year; variable capital is the wages bill, which is equal to the capital represented by the wages fund.) Surplus is equal to variable capital (net income is divided equally between wages and surplus) and half of surplus is saved.[19] Savings are allotted between constant and variable capital in such a way as to preserve the 4 to 1 ratio. Thus four-fifths of savings represents a demand for producers' goods, and is added to constant capital each year, and one-fifth represents a demand for consumers' goods, and is added to the wages fund (variable capital). These ratios dictate the relationship between Department I (producers' goods) and Department II (consumers' goods).[20] It can easily be seen that the basic assumptions require that the output of Department I must stand in the ratio of 11 to 4 to the output of Department II.[21] We can now construct a much simpler model than those provided in the text. _c_ _v_ _s_ _Gross Output_ Department I 44 11 11 66 Department II 16 4 4 24 -- Total 90 In Department I, 5·5 units are saved (half of _s_) of which 4·4 are invested in constant capital and 1·1 in variable capital. In Department II 2 units are saved, 1·6 being added to constant and 0·4 to variable capital. The 66 units of producers' goods provide 44 + 4·4 constant capital for Department I and 16 + 1·6 constant capital for Department II and the 24 units of consumers' goods provide 11 + 4 wages of labour already employed, 5·5 + 2 for consumption out of surplus, and 1·1 + 0·4 addition to variable capital, which provide for an addition to employment. After the investment has been made, and the labour force increased in proportion to the wages bill, we have _c_ _v_ _s_ _Gross Output_ Department I 48·4 12·1 12·1 72·6 Department II 17·6 4·4 4·4 26·4 ----- Total 99 The two departments are now equipped to carry out another round of investment at the prescribed rate, and the process of accumulation continues. The ratios happen to have been chosen so that the total labour force, and total gross output, increase by 10 per cent per annum.[22]