"It is difficult to say who it was who first recognized the advantage of always equating to zero in the study of the general equation. It may... have been Napier, for he wrote... De Arte Logistica before 1594 (although... first printed... 1839), and in this there is evidence that he understood the advantage... Bürgi (c. 1619) also recognized the value of making the second member zero, Harriot (c. 1621) may have done the same, and the influence of Descartes (1637) was such that the usage became fairly general."