Second half of 17th cent.
Brass; diameter 9,4 cm; max. length 11,8 cm
Florence, Istituto e Museo di Storia della Scienza, inv. 1312

Instrument designed by Viviani, whose drawing was found in his notes. The device made it possible to develop coded languages through the coordinated substitution of the letters of the alphabet shown by the index arm and the index of the smaller disk.