An alteration of the classic complexometric titration of calcium and magnesium with EDTA was made to incorporate a laser photometer for endpoint detection. The photometer utilized a He-Ne laser, which allowed the red to blue transition of the calgamite indicator to be followed by monitoring the change in beam absorbance. A photodiode and an inexpensive computer interface were used to record the intensity of the transmitted laser beam as a function of time. This method makes the experiment much more accessible for students suffering from color blindness.

Procedure to determine radon levels in water.