As unity within its circuits, as value in motion, whether in the
 sphere of production or in either phase of the sphere of circulation, capital
 exists ideally only in the form of money of account, primarily in the mind
 of the producer of commodities, the capitalist producer of commodities.
 This movement is fixed and controlled by book-keeping, which includes the
 determination of prices, or the calculation of the prices of commodities.
 The movement of production, especially of the production of surplus-value
 — in which the commodities figure only as depositories of value, as the
 names of things whose ideal existence as values is crystallised in money
 of account — thus is symbolically reflected in imagination. So long as
 the individual producer of commodities keeps account only in his head (for
 instance, a peasant; the book-keeping tenant-farmer was not produced until
 the rise of capitalist agriculture), or books his expenditures, receipts,
 due dates of payments, etc., only incidentally, outside of his production
 time, it is palpably clear that this function and the instruments of labour
 consumed by it, such as paper, etc., represent additional consumption of
 labour-time and instruments which are necessary, but constitute a deduction
 from the time available for productive consumption as well as from the
 instruments of labour which functions in the real process of production,
 enter into the creation of products and value.[12] The
 nature of the function is not changed — neither by the dimensions which
 it assumes on account of its concentration in the hands of the capitalist
 producer of commodities and the fact that instead of appearing as the function
 of many small commodity-producers it appears as the function of one capitalist, as a function within a process of large-scale production; nor is it altered
 by its divorcement from those productive functions of which it formed an
 appendage, nor by its conversion into an independent function of special
 agents exclusively entrusted with it.