Today, I tried a new lab practicum based on The Physics Teacher article, “Determining the Thickness and Refractive Index of a Mirror.” Through careful measurements of the reflected and refracted beams and graphical analysis, students determine both the thickness of the mirror and the index of refraction. The most challenging part of the lab was keeping everything aligned and accurately measuring the angle. The use of the level app on a smartphone made measuring the angle much easier. My first class struggled to make accurate measurements as we were trying to keep the laser level and angle the mirror and screen. After watching one group during first hour try various techniques, I encouraged second hour to take a different approach. They changed the angle of the laser and left the mirror flat on the table. This approached resulted in more accurate measurements.