Quantum draws the tiny lines which were later called the increments in the triangle characteristic of a curve and then gives the instruction, as a mere rule, to eliminate as superfluous the terms which, as a result of the expansion of the equations, turn up as the powers of such increments or as products (etenim isti termini nihilum valebunt); similarly to omit the terms which contain magnitudes only determined by the original equation (the subsequent subtraction of the original equation from the one construed with the increments), and finally to substitute, for the increment of the ordinate, the ordinate itself, and, for the increment of the abscissa, the subtangent.