Metrology Glossary – O

At J.A. King, we strive to educate our team and our customers so we can all make informed decisions and improve quality. Having information at our fingertips is the best way to do that. We have compiled a list of the most common terminology within the precision measurement industry, backed by our experts with years within our industry.

Precision Measurement Glossary of Terms

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Office of Weights and Measures (OWM)

Office at NIST that ensures consistency in any laws, regulations or standards regarding weights and measurements


The SI unit of electrical resistance, equal to the amount of resistance in a circuit energized with one volt of potential difference and transmitting a current of one ampere.

Ohm Meter

Any of a variety of tools which measure electrical resistance, the opposition to an electrical current. Many ohmmeters are specialized to read either very low resistance (micro-ohmmeter) or very high resistance (megohmmeter).

Ohm’s Law

An equation that describes how current, resistance and voltage are related. I=E/R where R is resistance, I is current and E is voltage

Optical Comparator

A device that applies the principles of optics to the inspection of manufactured parts

Optical Flat

An optical-grade piece of glass lapped and polished to be extremely flat on one or both sides, usually within a few tens of nanometres (billionths of a meter). Used as a reference against which the flatness of an unknown surface may be compared.


Also known as optical coupler, optocoupler and opto-isolator, a semiconductor device that uses a short optical transmission path to transfer an electrical signal between circuits or elements of a circuit, while keeping them electrically isolated from each other.

Original Equipment Manufacturer (OEM)

The original company who manufactured the equipment. Typically the equipment is used as parts in other equipment by other manufacturers and then resold


A device measures voltage as a function of time, allowing an AC current (via a special probe) or voltage to be displayed as an oscillating waveform.


The signal produced by a device when an input is applied. Often, transducers and load cells output a voltage or current which can be measured by a meter and scaled with the circuitry in the indicator to provide a reading in the desired unit of measure.

Over Range

Exceeds the full scale reading but does not exceed maximum safe overload capacity.


The load beyond full-scale value that an instrument can withstand without damage or failure. Usually expressed as a percent of a full-scale value.

Overload Rating (Safe)

The maximum weight that can be put on a scale before it permanently alters performance of the scale.

Overload Rating (Ultimate)

The maximum weight that can be put on a scale before it is damaged structurally.


The ratio of the overtravel of the pointer beyond a new steady deflection to the change in steady deflection when a new constant value of the measured quantity is suddenly applied.

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