To span the great distance from the solar system to the farthest clusters of galaxies in the universe, astronomers break down the distance indicators into steps. The nearest ones are measured geometrically, with what is known as parallax. Among the objects whose distances are thus directly measured are a rare type of star known as a Cepheid variable. To provide students with hands-on lab experience in deriving Leavitt's law--formerly the period-luminosity relation--each hour exam and final exam reveals that some students haven't been able to follow the logic. The authors believe that understanding the reasoning that leads to what is now called the Hubble-Lemaître law is fundamental to being well-educated in astronomy. To show students the logic and reasoning that goes into assessing the mathematical model that describes the traditional expansion of the universe (ignoring its acceleration), now known as the Hubble-Lemaître law, the authors stress a few critical-thinking arguments, one of them how to use Cepheid variables to find the distance to a galaxy. To emphasize visual learning, helping make the relevant concepts concrete, the authors describe in this article how to make a small box with switches to turn on lights to match the shape of the light curves (with a sharp rise and a slower fall) and the periods of Cepheid variables.