12 – b x v t S a – 2 9 7 3 y – d 9 7 6 5 - p o n n – e K i h – f 8 t r q g c

S – K h r – m r q p o K n c e a – m S r q p o K n – n d f b

Your master template shall be the figure a c b d, made a hundred braccia long, and let a c be one finger's width; and follow the two lines a b c d as far as r h, and cut a thin little board in the very shape of r h a c. Then move that board into h c K n, placing side r a onto h c, and side h c will come to rest on K n. But it would be better to have two like boards and set one in contact with the other, and so go on exchanging them to the end. And such boards ought to be at least two braccia long; and do the same below at b d; and then those lines b a d c would meet at the point S, and so would all of them.

Let angle b be equal to angle d, and likewise let the upper angles at a and c be equal to each other. Then let side a b be equal to side c d, and let side a b be set perpendicular upon the line b n, and let angle d be in contact with that line b n, whence for this reason angle d will lift away from that line b m; and from here we take the rule for the curved line b m, which has already, at d, parted from the line b n, which is our purpose. This done, we...