Chemical Education Today
From Past Issues
Old Friends: Slide Rules and Such
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Preparing this month’s From Past Issues prompted me to visit an old friend. But I didn’t have to travel far. For years, my friend has waited patiently in my center desk drawer. There, partially hidden under a stack of rubble, lay my longneglected slide rule. At one time I could choose from three of these sleek accessories: an enameled wooden K&E (Keuffel & Esser) similar to the Dietzgen shown in Figure 1, a circular version made of metal, and a plastic Aristo-Multilog. The K&E warped to uselessness in the indoor/outdoor temperature extremes of college-day winters, and I either lost or gave away the “more precise” circular one. But I can still depend on the Aristo. Its less elegant construction remains unwarped, although the glued crack at one end testifies to the mortality of any material. A hand-me-down from my brother, the Aristo lacked a protective cover until I put my seamstress skills to work on some scraps from a blue skirt. Numerous articles on slide rule pedagogy and applications have appeared in the Journal—ten search hits prior to the early 1980s when low-cost calculators became available. But I was actually researching another topic when I felt the need to visit my once essential “slipstick”. Leafing through volume 25 (1948), I came upon a oneand-a-half page article entitled “A Device for Adjusting Grades” (1). It captivated my curiosity. Author William Ehret of New York University presented his solution to a problem faced by many of us who teach large, multisection courses— adjustment of exam grades to a common average. He used a
Figure 2. Ehret’s graph for grade adjustment to a 75 average (1). The actual class average (57 in this example) on the bottom scale of the ruler aligns with the ray AB that passes through 75,75 on the nomograph. The grader locates individual scores on the ruler and follows the closest ray to the new grade on the horizontal line.
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Photo by Jerrold J. Jacobsen
by Kathryn R. Williams
Figure 1. A slide rule classic still in use in the 21st century.
graphical approach, explained briefly with the photograph reproduced in Figure 2. Ehret also demonstrated the method to his students, “…for nothing helps student morale more than to know that all are treated alike and as fairly as limitations of the procedure will allow.” Ehret’s paper reminded me of the days when we used to tack nomographs for a variety of quick conversions to bulletin boards and convenient locations in the laboratory. Interested readers can find a half-dozen chemistry-related examples by searching the JCE Index for “nomograph” in the title field. But if you want a beautiful turn-on for your class, I suggest checking a book on optical mineralogy for a chart of interference colors. So, what is the connection to my Aristo-Multilog? Aroused by Ehret’s article, I consulted the online index for titles containing “grade” or “grading”. Pre-1948 works focussed primarily on laboratory grades, but a flurry of papers and letters about grade adjustment (2–6) appeared within two years of Ehret’s publication. When I looked up the contribution by Ralph Seifert, my eyes immediately focussed on the picture reproduced in Figure 3—a modified slide rule. Hence the need to unearth the old friend in my desk drawer. Citing Ehret’s work, Seifert showed mathematically that the same principle was “involved in the method which was devised by the author (i.e., Seifert) 12 years ago and has been used by him during 10 years of teaching.” As shown in the picture, he renumbered the A and B scales from 99 to zero (instead of two decades from 1 to 10). By aligning the raw class average (57 to correspond to Ehret’s example) on the B scale with the target average (75) on the A scale, Seifert could read the corrected student grade (A scale) for any raw score (B scale). If you’re thinking that I’ve overlooked the numerous grading procedures described in the second half-century, you’re right. Computers and packaged software have long replaced slide rules and nomographs for most computations,
Journal of Chemical Education • Vol. 77 No. 4 April 2000 • JChemEd.chem.wisc.edu
Chemical Education Today
Figure 3. Seifert’s modified slide rule for adjusting grades (4). The A and B scales are renumbered as shown. The actual class average (57) and raw scores on the B scale align with the target average (75) and adjusted scores on the A scale.
including statistical grade adjustment. But it was Seifert’s slide rule method that led me to resurrect the companion I held in my hands for so many years. The introductory paragraph relates only a few of the memories inspired by my AristoMultilog and its handmade case. Go dig out your own (or an older colleague’s) slipstick. It is sure to provoke thoughts of life in the BC (before computers) era. W
Supplemental Material
References 1 and 4 have been reproduced and are available in this issue of JCE Online.
Literature Cited 1. 2. 3. 4. 5. 6.
Ehret, W. S. J. Chem. Educ. 1948, 25, 690–691. Horton, W. S. J. Chem. Educ. 1949, 26, 286. Ehret, W. F. J. Chem. Educ. 1949, 26, 287. Seifert, R. L. J. Chem. Educ. 1949, 26, 381–382. Ehret, W. F. J. Chem. Educ. 1949, 26, 394. Little, M. H. J. Chem. Educ. 1950, 27, 267–268.
Kathryn R. Williams teaches in the Department of Chemistry, University of Florida, P. O. Box 117200, Gainesville, FL 32611-7200; email:
[email protected].
JChemEd.chem.wisc.edu • Vol. 77 No. 4 April 2000 • Journal of Chemical Education
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