The right-hand side of this equation is the sum of terms of the form _pQ_--a price multiplied by a quantity bought. It is customary in mathematics to abbreviate such a sum of terms (all of which are of the same form) by using "Sigma" as a symbol of summation. This symbol does not signify a _magnitude_ as do the symbols _M, V, p, Q_, etc. It signifies merely the _operation_ of addition and should be read "the sum of terms of the following type." The equation of exchange may therefore be written: _MV_ = Sigma_pQ_. That is, the magnitudes _E_, _M_, _V_, the _p_'s and the _Q_'s relate to the _entire_ community and an _entire_ year; but they are based on and related to corresponding magnitudes for the individual persons of which the community is composed and for the individual moments of time of which the year is composed. The algebraic derivation of this equation is, of course, essentially the same as the arithmetical derivation previously given. It consists simply _in adding together the equations for all individual purchases within the community during the year_.... [We are now] ... prepared for the inclusion of bank deposits or circulating credit in the equation of exchange. We shall still use _M_ to express the quantity of actual money, and _V_ to express the velocity of its circulation.[46] Similarly, we shall now use _M'_ to express the total deposits subject to transfer by check; and _V'_ to express the average velocity of circulation. The total value of purchases in a year is therefore no longer to be measured by _MV_, but by _MV_ + _M'V''_. The equation of exchange, therefore, becomes: _MV_ + _M'V'_ = Sigma_pQ_ = _PT_[47].... With the extension of the equation of monetary circulation to include deposit circulation, the influence exerted by the quantity of money on general prices becomes less direct; and the process of tracing this influence becomes more difficult and complicated. It has even been argued that this interposition of circulating credit breaks whatever connection there may be between prices and the quantity of money.[48] This would be true if circulating credit were independent of money. But the fact is that the quantity of circulating credit, _M'_, tends to hold a definite relation to _M_, the quantity of money in circulation; that is, deposits are normally a more or less definite multiple of money.