In many industries, precise and accurate measurements are essential for maintaining product quality, ensuring safety, and optimizing operational efficiency. Over time, however, even the best equipment can experience a drift in accuracy due to factors like environmental conditions, wear, and natural degradation. This is where equipment calibration becomes critical. Calibration not only verifies and corrects measurement accuracy but also helps organizations meet regulatory standards and uphold best practices. This guide explores the fundamentals of equipment calibration, why it matters, and how it contributes to the reliability and effectiveness of industrial processes across various fields.

Fluke 9500C set up for calibrating oscilloscopes
What Is Equipment Calibration?
Equipment calibration, sometimes also called machine calibration, is the act of comparing a Device Under Test (DUT) of an unknown value with a reference standard of a known value. A person typically calibrates equipment to determine the error of its measurements or to verify the accuracy of the DUT’s unknown value. Calibration typically involves the use of a measuring standard to make comparisons at specified measurement points on the DUT.
Bureau International des Poids et Mesures (BIPM) is the coordinator of the worldwide measurement system that is tasked with ensuring worldwide unification of measurements. BIPM defines calibration as an “operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.”
Why Is Equipment Calibration Important?
Although most people don’t realize it, thousands of calibrations are conducted every day around the world to keep equipment and machinery up and running safely, efficiently, and according to the manufacturer’s specifications.
Calibration fosters and improves scientific discovery, industrial manufacturing, and international trade. That’s why most equipment should be calibrated regularly to prevent failure in production and during use.
What Are the Types of Equipment Calibration
There are many calibration disciplines, each with different types of calibrators and calibration references. To get an idea of some of the types of calibrators and instruments available, see the wide array of Fluke calibrators and other calibration equipment.
Common calibration disciplines include but are not limited to:
In general, the equipment that requires calibration is depended on to provide accurate, reliable measurements. Different levels of calibration can be performed depending on whether the equipment calibration must be traceable to national standards (“accredited” calibration) or to a standard calibration that does not take measurement uncertainty into account. Both types of calibration typically result in a calibration report, and the accredited calibration typically also includes the logo of the accrediting body.
What Is the Equipment Calibration Process?
There are several ways to calibrate an instrument, and the appropriate way depends on the type of instrument and the chosen calibration scheme. Here are a few examples of general calibration schemes:
- Calibration by comparison with a source of known value: In this type of calibration, the operator compares the accuracy of a measuring instrument with that of a standard over a series of specified measurement points. The standard should typically be three or four times more accurate than the measuring instrument. An example of a source calibration is measuring an ohmmeter using a calibrated reference standard resistor. The reference resistor is the source that provides a known value of the ohm, the desired calibration parameter. A multifunction calibrator can also be used as the source to provide known values of resistance, voltage, current, and other electrical parameters.
- Calibration by comparison of the DUT measurement with the measurement from a calibrated reference standard: A variant of source-based calibration is calibrating the DUT against a source of known natural value, such as a chemical melt or freezing temperature of a material like pure water (e.g., triple point of water cell).
- Calibration by characterization: Non-adjustable instruments, sometimes referred to as “artifacts” — such as temperature RTDs, resistors, and Zener diodes — are often calibrated by characterization. This usually involves some type of mathematical relationship that allows the user to use the instrument to get calibrated values.
- Simple error offsets calculated at different levels of the required measurement, like different temperature points for a thermocouple thermometer
- Slope and intercept correction algorithmsin digital voltmeters
- Complicated polynomialssuch as those used for characterizing reference standard radiation thermometers
A calibration process starts by comparing a known measurement with an unknown. This lets you determine the error or the value of the unknown quantity. Depending on whether the DUT is within or outside of the manufacturer’s specifications, the operator may repair the equipment until it operates within specifications. For example, measurement devices might be adjusted physically (turning a screw on a pressure gauge), electrically (turning a potentiometer in a voltmeter), or by adjusting internal firmware settings in a digital instrument.
Alternatively, the operator could conduct an “as found” and “as left” verification, which indicates the level of error but does not perform repairs. The “as left” verification step is required any time an instrument is adjusted to ensure the adjustment works correctly. Artifact instruments are measured “as-is” since they can’t be adjusted, so the “as found” and “as left” steps don’t apply.
For some devices, calibration data is maintained on the device as correction factors, where the user compensates for the known correction when using the device. It is generally assumed that the device in question will not drift significantly, so the corrections will remain within the measurement uncertainty provided during the calibration.
Equipment calibration is a vital process that ensures the accuracy and reliability of measurement instruments across industries. Regular calibration not only maintains the integrity of scientific and industrial processes but also promotes safety, efficiency, and compliance with international standards.
By understanding the different types of calibration and adhering to best practices, organizations can minimize errors, reduce downtime, and enhance overall operational performance.