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containing two or more sets of precision resistors mounted on ten-position rotary selector switches.
A typical decade resistance box may have one switch with resistors having values of between 0.1
and 0.9 ohm and another switch with resistors having values of between 1.0 and 9.0 ohms. A third switch
may have resistors with values of between 10.0 and 90.0 ohms.
By the proper positioning of the three switches, any value of resistance between 0.1 ohm and 99.9
ohms may be selected.
decalage. The difference in the angles of incidence between the two wings of a biplane. If the upper wing
has a greater angle of incidence than the lower wing, the decalage is positive. If the lower wing has the
greater angle of incidence, the decalage is negative.
decarbonizer. A solvent used to soften carbon deposits that have formed on metal surfaces. Carbon formed
on engine parts because of the coking action of oil is hard and is baked onto the surface of the metal. It
must be softened with a decarbonizer before it can be removed.
Some decarbonizers are used cold, and others are heated to make them act faster.
decay (condition of vibrations). To gradually decrease the amplitude of vibrations. A damped oscillation
is one in which the amplitude of the oscillations decay, or become less with time. See damped oscillation.
decay (wood defect). The breakdown, or decomposition, of the structure of wood fibers. Wood that shows
any indication of decay must be rejected for aircraft structure.
Decca navigation system. A long-range, hyperbolic navigation system that allows a navigator to establish
a line of position by measuring the phase difference between a master signal and three slave signals.
These medium-frequency continuous-wave signals are transmitted simultaneously from a
land-based master station and three slave stations.
Printed from Summit Aviation's Computerized Aviation Reference Library, 2/7/2007
Page 178
decelerate. To decrease the speed of a moving object; to slow it down.
deceleration. The amount the velocity of an object, measured in feet per second, is decreased by a force
during each second it is acted upon by that force. Deceleration is normally expressed in terms of feet per
second, per second (fps2).
deci. The metric prefix that means one tenth. For example, a deciliter is one tenth of a liter.
decibel (acoustic measurement). The basic unit of sound intensity equal to one tenth of a bel. For practical
purposes, one decibel (abbreviated dB) is the lowest amount of sound pressure that can be heard by a
normal human ear. Sounds above about 130 decibels normally cause pain.
decibel (electrical measurement). A measurement of the ratio of two electrical powers. One decibel is
equal to ten times the logarithm of the ratio of the two powers. See bel.
deciduous. A type of tree that sheds its foliage at the end of the growing season. Hardwoods come from
deciduous trees.
decimal digit. Any of the Arabic numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
decimal fraction. A proper fraction whose denominator is a number which is a power of ten. The value of
the denominator is not written, but it is indicated by the position of the decimal point.
One digit to the right of the decimal point means that the denominator is 10 (0.1 = 1/10); two
digits to the right of the decimal shows the denominator is 100 (0.01 = 1/100), and three digits indicates
1,000 (0.001 = 1/1,000).
decimal number system. The system of numbers using ten as its base. The digits in the decimal number
system are 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. In a multidigit number, the position of the digit shows its value.
Each position has a value ten times that of the position immediately to its right. For example, the number
5,286 is the same as 5,000 (5 • 1,000) + 200 (2 • 100) + 80 (8 • 10) + 6 (6 • 1).
decimal point. A dot which separates a whole number from its decimal fraction. In the United States, the
decimal point is placed at the bottom of the number, as in 14.2. In European countries, the dot for the
decimal point is raised to the center of the number, as in 14•2.
decision altitude/decision height (ICAO). A specified altitude or height (A/H) in the precision approach
at which a missed approach must be initiated if the required visual reference to continue the approach has
not been established.
decision height (DH) (aircraft operation). 14 CFR Part 1: “The height at which a decision must be made,
during an ILS or PAR instrument approach, to either continue the approach or to execute a missed
approach.”
declination (navigation). The error in the indication of a magnetic compass caused by the magnetic north
pole not being at the same location as the geographic north pole.
　
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