Index of Refraction: With the Blackboard or Whiteboard Optics semicircle piece you can measure the index of refraction of the lucite material directly with Snell's Law This will be a useful value later if you plan to use the rectangular block for parallel deviation or the prism for total internal reflection. Then you can predict and check results from your measured value of n. See Blackboard Optics [1] and Measuring a Glasses Prescription [2].
Links:
[1] https://demoweb.physics.ucla.edu/node/362
[2] https://demoweb.physics.ucla.edu/node/367