Slide Rule

Even after engine dividing became widely available in the 20th century, roughly made logarithmic scales could be found on mathematical instruments. This device consists of a wooden box with a sloping lid. The box contains nine paper scales covered with tape.

The first scale is on the back edge of the box, equally divided from 0 to 80, and labeled ONES. The second scale is on a sliding wooden slat in front of the first scale, equally divided from 0 to 80 but with divisions twice as large as those on the first scale, and labeled TWOS. The third scale also slides, is equally divided from 0 to 70 (with divisions three times as large as the first scale), and is labeled THREES. The fourth scale is also on a sliding slat, is equally divided from 0 to 60 (with divisions four times as large as the first scale), and is labeled FOURS. The fifth scale is on a sliding slat and is equally divided from 0 to 40, with divisions six times as large as the first scale. It is not labeled.

In front of the four sliding slats is a fixed slat that spans the entire width of the instrument. It has two scales. The upper one is a scale of equal parts with divisions the same size as the top scale, but running from 0 to 240. It is labeled TOTAL (/) POINTS. The top five scales can be used to add units of 1, 2, 3, 4, and 6, with the total indicated on this scale.

The lower scale on the fixed piece is also numbered from 0 to 240, but it is divided logarithmically. A sliding scale in front of it is divided logarithmically from 5.6 to 1.5; it indicates points per hour. The scale on the front edge of the box is divided logarithmically. It runs from 10 to 80, and is labeled HOURS. The fixed slat is marked on its right end: Mfg. by (/) W. J. & W. L. (/) (All rights reserved). The instrument was found in South Junior High School in Bloomfield, N.J., a magnet school for the visual and performing arts that operated from 1939 to 1987.

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