* {{en}} J.S. Cramer, ''Velocity of circulation'', in [[The New Palgrave: A Dictionary of Economics]], vol. 4, 1987. Pagg. 601-602.
<!----------------------------------------------------------------------------* Friedman,{{en}} [[Milton; Friedman]], “quantity''Quantity theory of money”money'', in ''[[The New Palgrave: A Dictionary of Economics]]'' (1987), vvol. 4, pp1987. Pagg. 3-20.
<!----------------------------------------------------------------------------* von Mises, Ludwig Heinrich Edler. von Mises, [http://mises.org/Books/humanaction.pdf ''Human Action'' 4th edition (1966),] Chapter XVII “Indirect Exchange”, §2.
