Screw-held tilting mechanism with a heavier arm
A red-chalk device whose weighted arm a-n is kept from toppling by screws b and c
Drawn in red chalk is a triangular bracket carrying a vertical threaded spindle, its points labelled n, a, b and c. The accompanying note explains that a-n weighs more than n, so that if the screws b and c were removed the arm a-n would fall upside-down; one should therefore move b first, then screw it in and move c. The caption identifies the figure as a partial companion to the drawing on folio 15r.
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Screw-adjusted spindle in a bracket
A vertical threaded spindle is set in a triangular bracket and secured by two screws, b and c. The note prescribes the order of adjustment: move b first, then screw it in and move c.
Unbalanced arm held by the screws
Because the arm a-n weighs more than n, removing the screws b and c would let a-n topple over; the screws hold the heavier side in check.