In the model set out in chapter vi there is no technical progress (this is a drastic simplification made deliberately[6]) and the ratio of capital to labour is constant (as the stock of capital increases employment increases in proportion). Thus real output per worker employed is constant (hours of work per year do not vary) and real wages per man are constant. It follows that real surplus per man is also constant. So long as these assumptions are retained Marxian _value_ presents no problem. _Value_ is the product of labour-time. _Value_ created per man-year is constant because hours of work are constant. Real product per man year being constant, on the above assumptions, the _value_ of a unit of product is constant. For convenience we may assume money wages per man constant. Then, on these assumptions, both the money price of a unit of output and the _value_ of a unit of money are constant. This of course merely plasters over all the problems of measurement connected with the use of index numbers, but provided that the technique of production is unchanging, and normal prices are ruling, those problems are not serious, and we can conduct the analysis in terms of money values.[7] (Rosa Luxemburg regards it as a matter of indifference whether we calculate in money or in _value_.[8]) The assumption of constant real wages presents a difficulty which we may notice in passing. The operation of the capitalist system is presumed to depress the level of wages down to the limit set by the minimum subsistence of the worker and his family. But how large a family? It would be an extraordinary fluke if the average size of family supported by the given wage of a worker were such as to provide for a rate of growth of population exactly adjusted to the rate of accumulation of capital, and she certainly does not hold that this is the case.[9] There is a reserve army of labour standing by, ready to take employment when the capitalists offer it. While they are unemployed the workers have no source of income, but are kept alive by sharing in the consumption of the wages of friends and relations who are in work.[10] When an increase in the stock of capital takes place, more workers begin to earn wages, those formerly employed are relieved of the burden of supporting some unemployed relations, and their own consumption rises. Thus either they were living below the subsistence minimum before, or they are above it now. We may cut this knot by simply postulating that real wages per man are constant,[11] without asking why. The important point for the analysis which we are examining is that when employment increases the total consumption of the workers as a whole increases by the amount of the wages received by the additional workers.[12]