harrysfrags:
I am building a controller for a salt water reef aquarium that will turn on and off heaters, lights, fans, etc. based on the temperature of the water. I'm using DS18B20 sensors and I have three of them. In bench testing all three of them vary by up to 1 degree. In addition they all show higher than my standard thermometer on the wall although I can't really vouch for it.My question is: How do people "calibrate" the sensors? I can vary the output in code to agree with the wall thermometer. In practical use the temp should only vary by 3 or 4 degrees. Is there a practical "known accurate" thermometer to be used for calibration?
One method is to use 'known' temperature sources to validate/calibrate temp sensors. Boiling water (100C or 212F) and crushed ice baths (0c and 32f) are pretty easy standards to calibrate with, if your sensor is rated to the two temp values.
Other then that it's a "Man with one watch always knows the time, man with two watches never quite sure" situation. 
Lefty