6.4.2.2 Verify the calibration at least annually. The probe
shall be recalibrated, when the check value differs by more
than 0.01 °C from the last probe calibration. Verification can be
accomplished with the use of a water triple point cell, an ice
bath or other suitable constant temperature device which has a
known temperature value of suitable precision. See Test
Methods E563, E1750, and E2593 for more information
regarding checking calibrations.