Bell mechanism: pivot braced against the tower walls
A toothed-wheel device to keep a swinging bell from shifting in its housing
The central diagram works out a bell-tower mechanism: the pivot (polo) is to bear against the walls of the campanile on both sides so that the bell cannot wander from its seat when it is rung, while the toothed wheels labelled mn and op stay engaged in their notches. A second sketch at the foot of the sheet shows a related lever-and-catch device. The Ambrosiana's classification also links the sheet to geometrical work (the greatest common divisor and Euclid VII.1), pointing to further untranscribed material.
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Pivot held between the tower walls; wheels mn, op kept in their notches
The pivot is to touch the walls of the bell tower on one side and the other, so that when the bell sounds it cannot leave its place. Leonardo notes that the wheels mn and op will then not come out of the toothed notches drawn below. Reference letters n o - a - m p key the parts of the mechanism.
Further untranscribed geometrical notes
Beyond the transcribed mechanical note the sheet carries additional mirror-script that the transcription does not include. The Ambrosiana's classification associates the leaf with geometry and algebra, specifically the search for the greatest common divisor and Euclid Book VII, proposition 1.