Many terms have different meanings when used in relation to different
subjects. The definitions in this glossary of terms are meant to be used in
conjunction with the subject matter within this text.
ACCIDENTAL ERRORAny small error
accidentally incurred in a measurement. Unlike
systematic errors, accidental errors are not
governed by fixed laws. They are as likely to be
positive as negative, and the theory of probability
is based on the occurrence of these errors.
ACCURACYThe degree of conformity with a
standard or the degree of perfection attained in
a measurement. Accuracy relates to the quality
of a result and is distinguished from precision,
which relates to the quality of the operation by
which the result is obtained.
ACTUAL ERRORThe difference between the
accepted value and the measured value of a
ACUTE ANGLEAn angle of less than 900.
ADJUSTED POSITIONAn adjusted value for
the horizontal or vertical position of a survey
station, in which discrepancies due to errors in
the observed data are removed. This adjustment
forms a coordinated and correlated system of
ADMIXTUREA material other than water,
aggregates, and portland cement (including
air-entraining portland cement and portland
blast-furnace slag cement) that is used as an
ingredient of concrete and is added to the batch
immediately before or during its mixing.
ADSORBED MOISTUREIn soil mechanics,
the thin films of moisture that may surround and
cling to the individual particles in a soil mass
because of naturally occurring electrical attraction
of water molecules to the soil particles.
AGGREGATEAny hard, inert, mineral
material used for mixing in graduated fragments.
It includes sand, gravel, crushed stone, and slag.
AGGREGATE, COARSEAggregate that is
retained on the No. 8 sieve.
AGGREGATE, FINE-Aggregate that passes the
No. 8 sieve.
AGONIC LINEThe line along which the
magnetic declination is zero.
ALGEBRAThat branch of mathematics that
pertains to the relations and properties of numbers
by means of letters, signs of operation, and other
symbols. Algebra includes solution of equations,
polynomials, verbal problems, graphs, and so on.
ALIDADEThe part of a surveying instrument
that consists of a sighting device with index and
reading or recording accessories. 1. The alidade
of a theodolite or engineer transit is the part of
the instrument that includes the telescope,
micrometer microscopes or verniers, and
accessories. These are mounted on what is called
the upper motion of the instrument, and they
are used in observing direction or angle on the
graduated circle, which is mounted on the lower
motion. 2. The alidade used in topographic
surveying consists of a straightedge ruler carrying
a telescope or other sighting device, and it is used
in plotting a direction on the plane-table sheet.
If a telescope is used, the instrument is often called
a telescopic alidade.
ALTITUDE1. The vertical angle between a
horizontal plane and the line to the observed or
defined object. In surveying, a positive altitude