Liguid-in-Glass Thermometers

What is the difference between a "general purpose/calibrated" and a "certified" thermometer?

It is common for the words calibrated and certified to be used interchangeably. All thermometers are calibrated, but not all thermometers are certified. In order to manufacture a thermometer, the instrument must be calibrated against a reference standard such as NIST. Calibration during manufacturing establishes the guidelines for line and number placement on the glass.

If a thermometer is certified or NIST Certified, this means that after the instrument is manufactured, it is once again individually calibrated against a reference standard (NIST) at a specific point or points along the scale. The results of this special second calibration are recorded on an official report from the manufacturer. This report, or certification document, accompanies the certified instrument when purchased.