Keithley DMM6500 Manual page 123

DMM6500 6½-Digit Multimeter with Scanning Calibration and Adjustment Manual
Example 1
cal.verify.date = os.time({year=2018, month=9, day=5})
print(cal.verify.date)
Set the verify calibration date to September 5, 2018.
Verify the date. Example output:
Sep 5 2014 12:00:00.000
Example 2
cal.verify.date = os.time()
Set the calibration verification to the present date of the instrument.
Also see
cal.adjust.date
DMM6500-905-01 Rev. E June 2021
(on page 4-3)
Section 4: TSP command reference
4-11