Elements of an adopted reference orbit that approximates the actual, perturbed orbit. Mean elements serve as the basis for calculating perturbations.
Related Terms 
DIRECTIVITY FACTOR

PLAN EQUATION
The mathematical statement that horsepower plan/33,000, where p mean effective pressure (pounds per square inch), l length of piston stroke (feet), a net area of piston (square inches), and n number of cycles completed per minute.

NYQUIST'S THEOREM
The mean square noise voltage across a resistance in thermal equilibrium is four times the product of the resistance, Boltzmann's constant, the absolute temperature, and the frequency range within which the voltage is measured.

NOMINAL PASSBAND CENTER FREQUENCY
The geometric mean of the nominal upper and lower cutoff frequencies of an acoustic or electric filter.

MEAN STRESS
1. The algebraic mean of mean stress mean temperature difference the maximum and minimum values of a periodically varying stress. 2. See octahedral normal stress.

MEAN NORMAL STRESS
In a system stressed multiaxially, the algebraic mean of the three principal stresses.

KALMAN FILTER
A linear system in which the mean squared error between the desired output and the actual output is minimized when the input is a random signal generated by white noise.

HOLLANDFORMULA
Aformulausedtocalculate the height of a plume formed by pollutants emitted from a stack in terms of the diameter of the stack exit, the exit velocity and heat emission rate of the stack, and the mean wind speed.

HEAT QUANTITY
A measured amount of heat; units are the small calorie, normal calorie, mean calorie, and large calorie.

HALFTIDE LEVEL
A tidal datum midway between mean high water and mean low water. Mean sea level may coincide with halftide level, but seldom does; the variation is generally about 3 centimeters and rarely exceeds 6 centimeters. Also called MEAN TIDE LEVEL.
