If lived at an altitude of 2500' and tried this test it wouldn't work--the water would boil at 207.5°F.It also specifically states to use OIL but I'm not sure why). Heat the oil, and monitor the conductivity of the thermoswitch with a multimeter. It should open (conduct) at approximately 208 degrees
Of course, using oil is a huge fire hazard. And if any water drops into the hot oil, the water drop will flash into steam and blow hot oil on to you--and the hot oil sticks on the skin and burns deep.