Key Takeaways
- As-found data is the measurement recorded before any adjustments — it shows the condition of the instrument when received for calibration.
- As-left data is the measurement recorded after calibration is complete — it shows the condition of the instrument when returned to service.
- If as-found data shows an out-of-tolerance condition, the operator may need to evaluate whether previous inspections or tests performed with that instrument are still valid.
- Without as-found data, there is no way to determine when an instrument went out of tolerance or how long it may have been providing inaccurate readings.
- PHMSA inspectors look for both values to verify the instrument was tested before adjustment, adjusted if needed, and returned to service within tolerance.
What Is As-Found Data?
As-found data is the measurement data recorded when an instrument is tested before any adjustments or repairs are made. It shows the condition of the instrument at the time it was received for calibration — exactly as it was found in the field.
This is one of the most important data points in a calibration record because it establishes the instrument's accuracy at the end of its service period. The as-found reading is compared against the instrument's specified tolerance to determine whether the instrument was within acceptable limits during its last period of use.
- Whether the instrument was within tolerance when it was received for calibration
- Whether the instrument had drifted out of tolerance since its previous calibration
- Whether previous measurements performed with that instrument may have been affected
- Whether an out-of-tolerance condition existed — and for how long
What Is As-Left Data?
As-left data is the measurement data recorded after calibration adjustments or repairs have been completed. It shows the condition of the instrument when it leaves calibration and is returned to service.
The as-left reading establishes that the instrument was within tolerance at the start of its next service period. It is the baseline that confirms the instrument was suitable for use after calibration.
- That the instrument was adjusted or repaired as needed
- That the instrument was within tolerance when returned to service
- That the instrument is suitable for use in compliance-related measurements
Why Both Values Matter — and Why You Can't Have One Without the Other
A calibration record that only shows as-left data tells you the instrument was in good condition when it left calibration — but nothing about the condition it was in beforehand. A record that only shows as-found data tells you the condition going in but not the outcome coming out.
Both values are required to tell the complete story: the instrument arrived in this condition, it was adjusted (or found to be in tolerance already), and it left in this condition. That complete picture is what PHMSA inspectors are looking for.
Expert Note: A calibration record that simply says 'Pass' or 'Within Tolerance' with no as-found or as-left readings is not a complete calibration record. Without the actual measurement values, there is no way to verify what tolerance limits were applied, how much drift existed, or whether the instrument was near the edge of its acceptable range.
The Out-of-Tolerance Problem: Why As-Found Data Is Critical
If an instrument is found to be out of tolerance during calibration — based on the as-found reading — the operator may need to evaluate whether previous inspections, tests, or measurements performed with that instrument are still valid. This evaluation is often called an out-of-tolerance evaluation or impact assessment.
The as-found data is the starting point for that evaluation. It tells you the magnitude of the error at the time of calibration. Combined with the calibration history and the date of the previous calibration, it helps establish a window during which the instrument may have been providing inaccurate readings.
Without As-Found Data, Out-of-Tolerance Is Uncontrollable
Without as-found data, an out-of-tolerance finding is significantly harder to manage. There is no way to determine when the instrument went out of tolerance, what the magnitude of the error was, or which prior compliance measurements may have been affected.
When a PHMSA inspector finds an instrument out of tolerance and there is no as-found data in the calibration history, the scope of the problem is undefined. An undefined problem is harder to close than a documented one — and inspectors know this.
Expert Note: An out-of-tolerance condition with complete as-found history is a manageable compliance event. An out-of-tolerance condition with no calibration history is an open-ended one. Which scenario you want to be in during an inspection is not a difficult choice.
What PHMSA Inspectors Look for in Calibration Records
When reviewing calibration records during an inspection, inspectors will often look for the following to verify as-found and as-left documentation:
- As-found measurement values recorded before any adjustments were made
- As-left measurement values recorded after calibration was completed
- Documentation of any adjustments or repairs made during calibration
- Documentation of out-of-tolerance conditions with a corresponding evaluation or corrective action
- Calibration history showing the trend of instrument performance over time
Best Practices for As-Found and As-Left Documentation
Organizations with well-managed calibration programs follow these practices for as-found and as-left data:
- Record as-found data before any adjustments are made — never adjust first and record after
- Record as-left data after all calibration adjustments are completed
- Document the specific measurement values, not just pass/fail notations
- Document any adjustments or repairs made during calibration
- Document and evaluate out-of-tolerance conditions when they occur
- Maintain full calibration history for each instrument so trends are visible
- Keep calibration records organized and immediately accessible during audits
How Cambri Compliance Helps
Cambri Compliance helps organizations store calibration records including as-found and as-left data, track out-of-tolerance conditions, store calibration certificates and reports, and maintain calibration history so calibration documentation is organized and available during inspections and audits.
Stop Managing PHMSA Compliance in Spreadsheets
Cambri Compliance provides both audit-ready compliance software AND hands-on PHMSA consulting — built by a former utility calibration technician with 38+ years of real-world audit experience.