Eric Olson

As the proverb claims, Slopeometer was born out of necessity. It happened when I was teaching calculus but has since proven incredibly useful in a variety of ways--from a middle-school setting on up. The inspiration came when I kept tracing along the graph of a function while I asked my AP calculus students at each point to “imagine the slope of the tangent line” as it gradually changed--from negative to zero to positive--representing the values of the “derivative” of the function. When, after some puzzled looks from my students, I said “imagine a plumb bob, always pointing to the correct value as it changes slope…” the lightbulb moment happened. Over the weekend, after a trip to a building supply store, I was able to cut a semicircle out of a piece of plexiglass and mark it with appropriate numbers and fractions, then loosely fasten a gravity-activated indicator arm that did the pointing... and presto!--the Slopeometer. My students found it much easier to picture the process, often called “curve-sketching,” and apply it to their own work. My students found it so helpful. Slopeometer has since proven useful in many areas: from “best fit” regression lines, to estimating tangent ratios, to slope-fields for differential equations--but the device has shown to be especially useful when first introducing slope.