Permuted and Compound Proportion
Red-chalk Euclidean proportion worked in terms a, b, c, d
In red chalk Leonardo works through ratio theory, heading one group "permuted proportion" and setting the terms c 6, a 4, d 3, b 2 so that c is to a as d is to b. A second group, labelled "conjoined" (compound proportion), states that the result is proved with the same terms, working the ratios 6:4 and 3:2. The page is laid out as proportion bars with fractions and letter labels.
On this page
Permuted proportion in terms a, b, c, d
Under the heading permuted proportion the terms are set as c 6, a 4, d 3, b 2, so that the ratio c to a matches d to b. Leonardo adds that it is proved with its own same terms, the letters a, b, c, d labelling the magnitudes.
Conjoined (compound) proportion
A second working, labelled conjoined, compounds the ratios 6:4 and 3:2 through the fractions ranged along the proportion bars (6, then 3 9 8, 4 12, 3 4). It sets out to demonstrate the same proportion by its own terms.