Frequently Asked Questions and Definitions on Calibration

What is Calibration?

Calibration is the comparison of a measuring device against an equal or better standard. Typically the reference standard has a higher accuracy than that of the Unit Under Test (UUT). Calibration finds out how far off the UUT measurement is from the reference instruments measurement. All measuring devices can drift over time, calibration ensures the devices are reading within tolerance as well as identifying devices that are in need or adjustment, repair, or replacement.

Why calibrate?

Calibration ensures that your devices are measuring accurately. Instruments that are not calibrated on a regular interval may give false readings unknowingly to the end user. In some industries, calibration may be required by a governing agency or board. Often times these agencies will require up-to-date documentation showing the measuring devises have been tested. This document is the Calibration Certificate.

MDQ Calibration Labs Hard at Work Determining Accuracy of Test EquipmentWhen to calibrate?


If you do a mix of critical and non-critical measurements, an annual calibration should suit your needs for cost and reliability. The majority of our customer will calibrate on an annual basis.

Monthly, Quarterly, or Semi-Annually
If you are doing critical measurements (and doing them often), you may want to use a shorter calibration cycle.  Shorter time between calibrations means more reliable results.

Before and After A Critical Measuring Experiment

If you’re planning a project that requires precise measurements, having your device calibrated prior to the experiment is a good way to ensure your results will be true and accurate. Always plan ahead and calibrate the equipment you will be using beforehand and then store them so that they are not used before the test. After running your experiment you may want to have your equipment calibrated again. This will ensure that your results are accurate and that your device stayed within spec during your test.

After an Event or Exposure to Harsh Environment

If your instrument absorbed an impact such as being dropped on the ground, performing a calibration is a good way to ensure it is still measuring accurately. If your device is used regularly in a dusty or harsh environment, you might consider having it calibrated more frequently to ensure it is working as it should.

Calibration Terms

As Found Data

The reading of the instrument against the reference before any adjustments are made.

As Left Data

The reading of the instrument against the reference after adjustments have been made. Sometimes this data will show the same value as the “as found data”. This is the case if no adjustments were needed.

In Tolerance Condition
When an instrument performs within the manufactures stated specifications.

Out of Tolerance Condition
When an instrument does not perform within the manufacturers stated specifications. If a device is found to be out of tolerance, it will have to either be adjusted to bring it back into spec or replaced. Not all loggers or recording devices can be adjusted.


The method used to calibrate the devices.
Calibration Environment

The temperature and humidity that the laboratory is kept.

Types of Calibration

MDQ Calibration Lab offers two types of calibration. Both of these calibrations are done using the same procedures and quality management programs. The only difference between the two services is the amount of data that is included on the calibration certificate. Both calibration types include a certificate of calibration. The certificate will contain information about the product being calibrated, “as found” and “as left readings”, and what reference standard was used that is traceable to NIST. For ISO/IEC 17025:2017 calibrations, we also include uncertainty data.

ISO/IEC 17025:2017 Calibration

An ISO/IEC 17025:2017 calibration is a premium option that provides NIST Traceability as well as the uncertainty of measurement at each test point. ISO/IEC 17025:2017 is the most widely used conformity assessment standard by testing and calibration laboratories worldwide. MDQ Calibration Lab meets the requirements of this standard. We are technically competent to perform testing and calibration and to producing technically valid results. This accreditation is very difficult to attain and it sets MDQ Calibration Lab apart as one of the very few labs to offer this level of service.

NIST Traceable Calibration

NIST stands for the National Institute for Standards and Technology. They are the organization responsible for maintaining the master for different measurements. They keep the standard for temperature, humidity, as well as other measurements. All of our instruments are calibrated and traceable to NIST. Traceable to NIST means our standards can be traced directly to the master standard maintained by the NIST organization. More information on NIST can be found on

PJLA (Perry Johnson Laboratory Accreditation)

PJLA is an organization that accredits calibration and testing facilities like ours to the ISO/IEC 17025:2017 standard. They are recognized as a third party auditor for this standard in the United States and internationally. When a customer purchases our ISO calibration, the calibration certificate will have a PJLA accredited mark with our accreditation number on the certificate. More information about PJLA can be found at

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