The spec sheet (http://datasheets.maxim-ic.com/en/ds/DS18B20.pdf
) says accuracy is 0.5DegC.
It is a thermistor. From my past experience using $20-$40 thermistors, the interchangeability is 1DegC while accuracy is 0.5DegC or 1DegC. The spec sheet is not quoting interchangeability
You can't get better than around 1DegC. If you really want accuracy, you need a thermocouple.
Interchangeability: when two "identical" sensors are subject to the same temperature, their average difference in temperature reported.
Accuracy, when the same sensor is subject to the same temperature, the standard deviation of its fluctuating value.
So one sensor could keep reporting around 22DegC while another one keeps reporting around 23DegC. They are interchangeable around 1DegC.
I just checked here:http://www.netstate.com/states/geography/mapcom/co_mapscom.htm
Seems like 5,000ft is the norm of lots of places in Colorado.
According to this:http://www.csgnetwork.com/h2oboilcalc.html
Boiling point is 95DegC instead of 100 at that altitude. I think this is consistence with my memory. Most flat regions don't have to worry too much.