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Madrid Ms. I (BNM), fol. 121r and v (details)
"Measure the power of the screw by taking the proportion of the lever to its counterlever. The lever shall be measured from the center of the moving hand or force which turns the screw, to the center of the screw. The counterlever goes from the mentioned center to the middle of the opposite thread."
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Leonardo da Vinci
Madrid Ms. I