Keithley SourceMeter 2600 Series Reference Manual page 282

12-8 Instrument Control Library
Time and date values
Date/time values are represented as a number of seconds since some base.
There are three time bases:
1. UTC 12:00 am Jan 1 1970.
2. When the Series 2600 is powered on.
3. Time referenced to an event, such as the first reading stored in a reading
buffer.
Time can be represented as the number of seconds since UTC 12:00 am on
January 1, 1970. The commands that utilize this format are commands that
require an absolute time reference such as setting the calibration date.
Time can also be represented as the number of seconds since the unit was
powered on. The os.clock() function returns values in this format.
Representing time as a number of seconds will be referred to as "standard time
format." Note that because numbers are floating point numbers, the precision of
date/time values will decrease the farther the elapsed time gets from its reference
base. This decrease in precision is approximately 0.06ppm of the total elapsed
time. This precision is generally more accurate than the time base of the
instrument and should not present any problems. It is worth noting, however,
because you can directly see the affects as compared to the less obvious time-
base drift.
2600S-901-01 Rev. A / May 2006
Series 2600 System SourceMeters Reference Manual
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