Once you've launched the Interactive and resized it, experiment with the interface to become familiar with it. Observe how the laser can be dragged about the workspace, how it can be turned On (Go button) and Cleared, how the substance on the top and the bottom of the boundary can be changed, and how the protractor can be toggled on and off and repositioned. Also observe that there is an incident ray, a reflected ray and a refracted ray; the angle for each of these rays can be measured.