Reading and Interpreting Tolerances

Tcal is the temperature at which the instrument most recently received its full calibration. This is shown in the calibration certificate on file for the instrument.

In the case of the 3458A, it is possible to display this temperature value with a special keystroke sequence (CAL? 59 <ENTER>).

Most instruments do not store the value of their calibration temperature and you need to look it up in their records.