Modern instruments and methods of calculation : a handbook of the Napier Tercentenary Exhibition (1914)
Horsburg, E. M. (Ellice Martin), Napier Tercentenary Exhibition (1914 : Edinburgh, Scotalnd) · London : G. Bell · leaf 124
One ofthe firstnine machinesbuilt Fig. 34.—Early Type. … Fig. 35.—Modern Machine. ease, and accuracy of operation in the modern machine. Notable amongthese improvements is the duplex feature introduced a few years ago. Priorto its invention only one key could be operated at a time. This meant thatif a second key was struck before the one previously…
