One of the two categories of errors of observation and measurement, the other category being systematic error. Random errors are the errors which occur when irregular, randomly occurring conditions affect the observing instrument, the observer and the environment, and the quantity being observed so that observations of the same quantity made with the same equipment and observer under the same observing conditions result in different values of the observed quantity. Random errors depend upon (1) the quality of the observing instrument. (2) the skill of the observer, particularly, the ability to estimate the fraction of the smallest division or graduation on the observing instrument, and (3) randomly fluctuating conditions such as temperature, pressure, refraction, etc. For many types of observations, random errors are characterized by the following properties: (1) positive and negative errors of the same magnitude are about equal in number, (2) small errors occur more frequently than large errors. and (3) extremely large errors rarely occur. These properties of random errors permit the use of a mathematical law called the Gaussian or normal distribution of errors to calculate the probability that the random error of any given observation of a series of observations will lie within certain limits. Random error might more properly be called deviation since mathematically, the random error of an individual observation is calculated as the difference or deviation between the actual observation and an improved or adjusted value of the observation obtained by some mathematical technique such as averaging all the observations. Also called ACCIDENTAL ERROR, CHANCE ERROR, IRREGULAR ERROR, STATISTICAL ERROR.
Related Terms 
PHASESHIFTING TRANSFORMER
A transformer which produces a difference in phase angle between two circuits.

PHASE MARGIN
The difference between 180 and the phase of the loop ratio of a stable system at the gaincrossover frequency.

PHASEBALANCE RELAY
Relay which functions by reason of a difference between two quantities associated with different phases of a polyphase circuit.

ORTHOMETRIC CORRECTION
A systematic correction that must be applied to a measured difference in elevation since level surfaces at varying elevations are not absolutely parallel.

OCEAN THERMALENERGY CONVERSION
The conversion of energy arising from the temperature difference between warm surface water of oceans and cold deepocean current into electrical energy or other useful forms of energy. Abbreviated OTEC.

NOMINAL BANDWIDTH
The difference between the nominal upper and lower cutoff frequencies of an acoustic or electric filter.

NEWTON'S LAW OF COOLING
The law that the rate of heat flow out of an object by both natural convection and radiation is proportional to the temperature difference between the object and its environment, and to the surface area of the object.

MOLDING SHRINKAGE
Difference in dimensions between the molding and the mold cavity, measured at normal room temperature.

MOISTURE GRADIENT
The difference in exit gases and that of moisture at ambient air temperature.

MODEL REFERENCE SYSTEM
An ideal system whose response is agreed to be optimum; computer simulation in which both the model system and the actual system are subjected to the same stimulus is carried out, and parameters of the actual system are adjusted to minimize the difference in the outputs of the model and the actual system.
