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?