This applet is designed to teach students how bin widths (or the number of bins) affect a histogram. The data consists of observations of the duration (in minutes) for eruptions of the Old Faithful geyser in Yellowstone National Park. Students can interactively change the bin width by dragging the arrow underneath the bin width scale. For large bin widths, the bimodal nature of the dataset is hidden, and for small bin widths the plot reduces to a spike at each data point. Students are asked “”What bin width do you think provides the best picture of the underlying data?”” Code for employing this technique with other datasets is supplied.