Which method verifies a thermometer's accuracy at freezing and boiling points?

• A. Ice-water method (32°F/0°C)
• B. Boiling-water method (212°F/100°C at sea level)
• C. Both the ice-water method and the boiling-water method
• D. A calibration using room-temperature water

Answer: (C)

Verifying a thermometer’s accuracy relies on fixed reference points at known temperatures. The ice-water method establishes the freezing point at 0°C (32°F) by immersing the sensor in a well-mixed ice-water bath and ensuring it reads near 0°C. This checks the lower end of the scale and reveals any offset or slow response as the thermometer moves toward cold temperatures. The boiling-water method sets the heating reference at the boiling point, about 100°C (212°F) at sea level. Immersing the sensor in vigorous boiling water should show roughly 100°C, confirming accuracy toward the hot end.

Using both methods together gives a complete check across the thermometer’s range, revealing inconsistencies that might not show up with a single point. If only one fixed point were used, errors could go undetected at the other end of the scale.

Calibrating with room-temperature water doesn’t test against a fixed, known temperature point and won’t confirm accuracy at the critical freezing or boiling references; it might help verify responsiveness at ambient temperature, but it isn’t a substitute for verifying those fixed endpoints.