drawings, and in 1888 he computed mul-
tiples of pi (π) to prove the acceptability
of the design. This is often thought to
represent the first successful test of a
“modern” computer part.What is a troncet?
The troncet (or addiator) is credited to J.
L. Troncet of France, who invented the
device in 1889. He called it his Arithmo-
graphe. (In actuality, his work was based
on earlier designs that were first started
by Claude Perrot [1613–1688].) It was
used principally for addition and sub-
traction.
A troncet’s flat, mechanical, palm-
held calculator had three main compo-
nents: the part for the calculation, a sty-
lus, and a handle to reset the addiator.
By inserting the tip of the stylus into
notches along a metal plate, numbers
could be added by sliding either up or down strips of metal with numbers marked on
them. No gears or interlinked parts were involved. To “carry one” when the sum of
two digits was greater than ten, the stylus was moved up to and around the top of
the device.What is a slide rule?
The slide rule is a ruler-like device with logarithmic scales that allows the user to do
mathematical calculations. It is portable, with the most common slide rules using
three interlocking calibrated strips; the central strip can be moved back and forth rel-
ative to the other two. Calculations are performed by aligning marks on the central
strip with marks on the fixed strips, then reading marks on the strips. There is also a
“see through” sliding cursor with a hairline mark perpendicular to the scales, allowing
the user to line up numbers on all the scales.Sadly for mathematical traditionalists, the use of the slide rule was eventually
overtaken by the pocket calculator by the mid-1970s. But in other ways, this develop-
ment was welcome. The slide rule had two major drawbacks, especially for calcula-
tions in mathematics, engineering, and the sciences: It was not easy to add with the
356 device and it was only accurate to three digits.
Recognized for his connection to the famous differ-
ence engine, English mathematician Charles Bab-
bage had to abandon his elaborate plans for a
mechanical computer because the device was simply
too expensive. Library of Congress.