In the hands-on, guided-inquiry lesson presented in this article, high school students create, calibrate, and apply an affordable scientific-grade instrument (Lapp and Cyrus 2000). In just four class periods, they build a homemade integrated circuit (IC) digital thermometer, apply a math model to calibrate their instrument, and ask a researchable question that can be answered using the thermometer they create. This activity uses the 5E learning cycle—engage, explore, explain, elaborate, and evaluate—to help physical science students discover the many connections between math and science (Karplus 1979).