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Hassler's Slide Rule
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Hassler's Slide Rule

 Loaned by Ferdinand R. Hassler, V, Ardoth A. Hassler, and Linda Hassler Reynolds
This 26.8 in wooden slide rule has a tongue-and-groove construction. It may be missing a cursor. The scales were pressed into the shellacked wood with stamps. Lamp black, a pasty mixture of linseed oil and charred ivory, was then rubbed into the stamped depressions. Over time, the compressed wood fibers recoiled to their original position, pushing the lamp black up to create a seemingly embossed surface. The top slat of the rule has a wrap-around logarithmic scale for numbers 1 000 000 to 100 000 000 in 10 parallel lines. Above this there are linear scales for numbers 1 to 20 and 1 to 30. The logarithmic scale on the bottom slat is for numbers 1 000 000 to 1 000 000 000, also in 10 wrapped lines. The other side of the rule has a linear scale for numbers 1 to 10 above a wrap-around logarithmic scale for numbers 100 to 1000. Its bottom slat carries the same scale, but this is folded at the number 892 in order that the number 1 occupy a position at the center of the first of 10 wrapped lines of numbers. A linear scale for numbers 0 to 9 runs along the bottom edge of the rule. These scales would have been useful to a terrestrial or celestial cartographer, which indeed, Hassler was.

Detail of Slide Rule