In a twodimensional or elliptical error distribution, the measure of error as the radius of a circle of equivalent probability derived from the error ellipse. The error, expressed as l drms, is the square root of the sum of the error components along the major and minor axes of the probability ellipse. The use of radial error or drms error as a measure of error is somewhat confusing because the term does not correspond to a fixed value of probability for a given value of the error measure.
Related Terms 
PLUG METER
A variablearea flowmeter in which a tapered plug, located in an orifice and raised until the resulting opening is sufficient to handle the fluid flow, is used to measure the flow rate.

PHOTONEPHELOMETER
A nephelometer that uses a photocell or phototube to measure the amount of light transmitted by a suspension of particles.

PHOTOELECTRIC REFLECTOMETER
A reflectometer that uses a photocell or phototube to measure the diffuse reflection of surfaces, powders, pastes, and opaque liquids.

PHOTOELECTRIC PHOTOMETER
A photometer that uses a photocell, phototransistor, or phototube to measure the intensity of light. Also known as electronic photometer.

PHOTOELECTRIC FLUOROMETER
A device using a photoelectric cell to measure fluorescence in a chemical sample that has been excited (one or more electrons have been raised to higher energy level) by ultraviolet or visible light; used for analysis of chemical mixtures.

PACHYMETER
An instrument used to measure the thickness of a material, for example, a sheet of paper.

OUTPUTMETER
Analternatingcurrentvoltmeter connected to the output of a receiver or amplifier to measure output signal strength in volume units or decibels.

OUNCE
1. A unit of mass in avoirdupois measure equal to 1/16 pound or to approximately 0.0283495 kilogram. Abbreviated oz. 2. A unit of mass in either troy or apothecaries' measure equal to 480 grains or exactly 0.0311034768 kilogram. Also known as apothecaries' ounce or troy ounce (abbreviations are oz ap and oz t in the United States, and oz apoth and oz tr in the United Kingdom).

ORIFICE PLATE
A disk, with a hole, placed in a pipeline to measure flow.

OPTIMAL CONTROL THEORY
An extension of the calculus of variations for dynamic systems with one independent variable, usually time, in which control (input) variables are determined to maximize (or minimize) some measure of the performance (output) of a system while satisfying specified constraints.
