Devoid of writing.

f 25 – teeth 300 – m – n

It turns round 10 braccia — that is, the wheel of the cart — so that it comes to have a diameter of 3 and 4/22 braccia. And the proof is that this diameter, multiplied by 3 and 1/7 of itself, will be found to make exactly 10. And if you want a simple way to find the diameter of any circle, take a circle whose diameter is known, namely one of circumference 22 that has 7 of diameter; that diameter multiplied by 3 and 1/7 makes 22. Now say, by the rule of three: if 22 of circle gives me 7 of diameter, what will 10 of circle give me? Work it and you will find it gives you 3 and 4/22. Therefore, when the wheel of the cart has made one whole turn, it will have measured 10 braccia of ground, that is 1/300 of a mile, which is 3000 braccia; and the wheel m will only have moved the space of one of its teeth — which wheel has 300 of them — so it is plain that, when the wheel m has made one whole turn, the cart has measured exactly one mile of distance; and the wheel f will have moved only the space of one of its teeth, and the wheel n has done the same, which shows with its spoke each mile, no otherwise than the little hand of the clock shows its hours. But the wheel f, instead of showing, makes the ear hear the noise, or sound, made by a little stone dropped into a vessel fit to receive sound.

f – a 60 – b 50 – c 50 – g

The toothed wheel a is found to have 60 teeth, b has 50 of them and c 50. Now, for every step the man or the horse takes, the lever g strikes on the thigh of whoever carries it, and in its motion makes one tooth of the wheel a move, and the pawl f holds it so that it does not turn back. Therefore the wheel makes one whole turn with 60 steps, and in the same time the wheel b has moved only one tooth, because the pinion of a has but a single tooth. The wheel a turns round 5 once and has 12 teeth per oncia, which makes 60 teeth, and has a diameter of 1 and 13/22 once.