Fig. 424.—Opisometer.
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874.—Boucher Calculator, the invention of M. Alex. E. M. Boucher, engineer, of Paris.[66] This is one of the most convenient pocket calculators that a civil engineer can desire, being only of the size of an ordinary watch. The instrument was formerly made in France for this country in a very slovenly manner. It is now made in London by the author, of sound work and accurate centring, Fig. 425. It has face back and front. The front one, which is shown in the illustration, carries logarithmic scales of sines, numbers and square roots, and is made to revolve by turning the milled head placed under the handle, as the winder of a keyless watch. The back dial, which is fixed and does not revolve, has upon it a scale of equal parts giving the decimal parts of logarithms, and a logarithmic scale of cube roots. There are three index hands, one fixed on the side of the case over the front dial, as shown in Fig. 425, and one on each end of the central axis made to revolve simultaneously over the back and front dials by means of the milled head at the side of the case. Any operation involving multiplication, division, proportion, powers or roots can be performed approximately with great rapidity by the aid of this calculator, and it is practically as simple to use as an ordinary slide rule, as will be seen from the following explanation of its use:—
Fig. 425.—Boucher's calculator.
Fig. 426.—Stanley-Boucher calculator.
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Multiplication, using the second circle of divisions from the outside of the front dial:—Bring the first factor under the fixed index, set the movable index to 1, then bring the second factor under the movable index, and the product will be found under the fixed index.
Division is performed on the same scale as follows:—Bring the dividend under the fixed index, set the movable index to the divisor, then bring 1 to the movable index, and the quotient will be found under the fixed index.
For proportion the second circle is also used:—Set the first factor under the fixed index and set the movable index to the second one, then the proportionate equivalent of any number brought under the former will be found at the movable index.