What does the instrument reference distinguish?
Keysight's BenchVue DMM DC Current help describes autozero as subtracting a zero reading from subsequent measurements. Its separate null feature reports the reading minus a stored null value. The documented automatic null selection can use the first reading as that reference.
Commissioning Docs is independent and is not affiliated with Keysight. These are the meanings in that documented application, not universal button names or commands for every meter. The same page lists calibration separately. Neither a null operation nor its displayed zero is a calibration certificate.
Sources: Keysight: Keysight: primary reference checked 25 October 2026
How can a correct relative result be mistaken for absolute current?
Illustrative example. In a deliberately simplified fictional measurement, a signal is 10.00 mA and an internal additive offset is 0.01 mA. An ideal zero correction removes that offset, giving 10.00 mA. Subtracting a separately stored null value of 9.00 mA then gives a relative result of 1.00 mA.
The 1.00 mA difference does not mean the input current is 1.00 mA. This arithmetic only isolates the two subtraction operations. It does not model instrument uncertainty, timing, drift or a particular test setup, and it does not justify correcting a real result by assumption.
What should travel with the recorded value?
Keep the original export and display evidence. A lone number without its measurement state can lose the distinction between an absolute result and a difference.
| Record | Evidence or interpretation |
|---|---|
| Quantity | Function, unit and intended absolute or relative result |
| Instrument | Model, firmware and applicable manual |
| Autozero | Actual state and recorded zero process |
| Null | Enabled state, stored value and reference origin |
| Result | Original value with timestamp and measurement state |
| Acceptance | Approved method, criteria and qualified review |
How should an ambiguous commissioning record be resolved?
Ask the responsible test owner for the instrument configuration and original evidence. Do not silently add a guessed null value to an old report or disable a feature merely to obtain the expected number. If a repeat measurement is needed, it follows the approved method and safety process.
Keep this state check separate from calibration traceability and the acceptance criteria. This guide does not authorize connections or live testing. Engineering sign-off is performed only by the registered engineer on the job.
Common questions
What else should the bid team know?
Does null mean the input has no current?
No. A null result can be a difference from a nonzero reference.
Does autozero replace calibration evidence?
No. Preserve the required calibration and method evidence separately.
Can a missing reference be reconstructed from an expected answer?
No. Recover the actual settings and original record or refer the gap for qualified review.