Understanding Instrument Calibration Documentation: As Found vs. As Left

The Difference between As Found and As Left Data

Instrument calibration is the comparison of an unknown device against a reference standard to know the deviation of the unknown device from the standard. A commercial instrument calibration employs the OEM’s procedure using a reference standard that is at least four times more precise than the equipment being tested.

The most important principle in instrument calibration is to document the measurement as it was found and as it was left after making adjustments. The main purpose behind documenting both as found and as left data is to facilitate precise calculation of drift over time and ensure the instrument is holding calibration even over time. Excessive deviation from the reference standard indicates an impending failure. Knowing this is very crucial in any quality assurance program or predictive maintenance schedule.

Defining Important Instrument Calibration Terms  

As Found Data
This term refers to the measurement recorded before any adjustment or repair can be made.

As Left Data
As left data is the instrument reading taken after the necessary repairs and adjustments are made.

Found Left Data
This is the measurement data recorded for any item or instrument that does not need any repairs or adjustments. This term is appropriate for use only when an instrument has passed calibration testing without undergoing any modifications.

This term is used for an instrument that is rendered unusable for testing a specific function or a certain range or when it is incapable of being powered.

How Comprehensive Quality Management Systems Use Historical Data  

Quality assurance technicians track calibration data over time for different reasons. Accurate recordings of test findings and data trends are required for smooth operation of quality management systems. Facility managers use this data to determine if certain instruments are losing their accuracy and efficiency over time. This data also helps analyze conformance as a whole and enables quality assurance departments to make informed decisions regarding tooling and testing investments.

Instrument Calibration Pro Tip

Lab calibration services offer different levels of data with quality assurance and calibration services. As found data refers to the readings taken originally at different set points during the instrument calibration and as left data refers to the adjusted set points if the instrument is found out of tolerance. Certain lab equipment calibration services charge more for this information while other lab calibration services include this data in their pricing. So, if you need lab calibration services, make sure you ask for both as found and as left data because it is mandatory for ISO 9001 certified companies. This will ensure that every single standard and measurement can be traced to the applicable standards and if the instrument calibration is being performed by accredited lab calibration services, they must also issue a certificate.

For a full range of onsite lab calibration services that guarantee reliable results and meet all the requirements of the FDA and cGMP environments, Call 1-877-799-0922.

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