Impedance: The opposition in an electric circuit to the flow of an alternating current.

Index of Refraction: The ratio of the speed of light in a vacuum to its speed in a given substance.

Inductive Load: Electrical devices made of wound or coiled wire.

Influence Quantity: Any effect that may influence the uncertainty associated with a measurement value.

Inertia: The tendency of a body to maintain is state of rest or uniform motion unless acted upon by an external force.

Infinite: Subject to no limitation or external determination, extending indefinitely.

Initialization: Setting a system to a known state.

Inspection: The process of measuring, examining, testing, gauging, or otherwise comparing the unit with the applicable instruments.

Inspection by Attributes: Analog-to digital conversion.

Instability: An undesired change over a period of time, which change is unrelated to input, operating conditions, or load.

Interferometer: Any measuring instrument that uses interference patterns to make accurate measurements of waves.

Interpolation: Calculation of the value of a function between the values already known.

ISO: International Organization for Standardization.

Inversion: The condition that exists when both axes of an image are reversed.

Inverter: Any mechanical or electrical device for converting direct current into alternating current.