A weight distributed 4 to 1 between two cords of a balance
The line of equality equals the horizon; weight 5 gives four parts to cord b and one to a
A balance staff hangs from its midpoint under the point 5, its two arms each marked in four equal divisions. A spherical weight, also labeled 5, is slung by a cord from the end a (1), while a second attachment at b (4) lies one unit from the centre n, and a dotted plumb-line drops from n to c just above the weight. Leonardo argues that the weight burdens cord b more than cord a in the same proportion as the line of power nc lies nearer b than a, here giving four parts to b and one to a. He opens the page by equating 'the line of equality' with 'the line of the horizon.'
On this page
The line of equality and the horizon
A note at the head of the page states that the line of equality and the line of the horizon are one and the same. It fixes the horizontal reference against which the loaded balance is judged.
A weight shared between cords a and b
A weight labeled 5 hangs from a staff suspended at its middle, point 5, with each arm divided into four equal parts. The load reaches the staff by cords at a (1) and b (4), and a dotted line falls from the centre n to c just above the weight.
Four parts to b, one part to a
Leonardo reasons that the weight burdens cord b more than cord a in proportion as the line of power nc lies closer to b than to a. Because nc stands one unit from the centre, the weight gives four to b and one to a.