I once heated a known quantity of water in a microwave to calculate how much wattage was going into the water. This has been done to measure the power of lasers, and was suggested by Steve Hardy to heat 100 grams of water for 10 minutes in a vacuum flask (Thermos) and then the wattage is the temp rise * 0.7.
My water went from 19.83 to 37.78C in 10 minutes while the laser was at 26.5 mA.
So that is 12.5 watts.
This does not seem to be working. Maybe the water is reflecting much of that beam. Or maybe water vapor is absorbing the beam.
Has anyone compared these $100 meters to an expensive laser power meter?