Accurate results in measuring the wavelength of red light (diffraction method)

The picture above shows the measurement method based on the diffraction formula 

nl = d sin q

Students measure x (distance between the central and the first maximum) and L (distance between the diffraction grating and the screen).  Despite very simple methods, the results are accurate.  The table below presents the results.  Percent error is calculated between the experimental value and the 680 nm red diode laser.

Table by Nicole, Marya, and Rudemy.

Ceiling Lights through the Diffraction Grating

All the hard work!

The paper presented above (posted here with the author's permission) documents all the hard work that students put into measuring indicated quantities.  To me, that paper has a lot more value than a nice copy of the results. It shows all the struggles, trials, errors, and victories on the way to understand the nature of sound phenomena.  

The challenge associated with this approach to learning is that the students must go through some confusion at first to finally come to better clarification.  If accepted, that challenge leads to knowledge based on experience - way above the knowledge from a textbook or a lecture.