Also, from what I understand, thermometers are most accurate in the range they are designed for ..... In other words, a body temp. thermometer is most accurate in normal body temp. ranges, while a meat thermometer works best on much higher temps.

I learned this from hatching baby chicks, where a precise temperature is critical to a successful hatch.

Either ice water, or a boiling water bath, depending on altitude, may give an accurate reading around 32*, and 212*, but if your water temp. is somewhere in the middle of these temps., accuracy will probably suffer.