Simple, compact, lasercut colorimeter

This simple colorimeter was inspired by this one:
http://www.sciencebuddies.org/science-fair-projects/project_ideas/Chem_p075.shtml#procedure
The webpage above contains a great suggestion on how to use the colorimeter with students too.
The cuvette rack I've published earlier is used by students to keep the cuvettes safe when using this colorimeter. I use it at work for high school students. They try to determine the concentration of brilliant blue (E133, CI 42090) in mouthwash after making a calibration graph based on a known solution of brilliant blue. The instrument is primitive, yet demonstrates the principle of colorimetry beautifully. The simple, primitive construction of the instrument opens up for interesting discussion and suggestions for refining the experiment, enhancing the learning experience. The experiments it can be used for combines maths, physics, electronics and chemistry nicely. I really like this little gadget. It's a gem.