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Instrument type

Folding Rule
Later 16th century; English
Brass; 425 mm in length

The instrument consists of a graduated arc of 90 degrees, and two pivoted arms, one fixed to the arc, the other sliding along it. The arc is divided to 10, to 5 and to 1 degrees, numbered from 5 to 90 by 5. The arm to which the arc is fixed is engraved with an equal scale, from 10 to 740, divided to 1 and to 1/2 units, numbered from 10 to 740 by ten. Ten units are slightly more than 5 mm. On the leg are pierced four additional holes, two of which are close to the arc, one at about 5.5 cm from the hinge, and the other at about 3 cm from the end of the arm.

The other arm has similar holes except for the one close to the hinge and has a screw system to adjust the arc. It is not engraved.

Ilaria Meliconi

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 599

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