Leica MX400 Operating Instructions Manual page 212

Glossary
A flashing rectangle superimposed on a character position in the
display window, indicating that a character may be entered in
that position, or that the existing character may be changed via
the keyboard.
DATUM
The framework on which the coordinates used to define position
on the earth's surface are based. In the navigator, a datum is
defined by the following parameters:
A and I/F. Size and shape of a reference ellipsoid.
DX, DY, DZ. Position of the reference ellipsoid origin in
relation to the satellite datum ellipsoid origin.
DEAD RECKONING
The process of determining changes of position based on
measured speed and course over measured time periods.
DECCA LINES OF POSITION (LOPs)
The phantom Decca Lines of Position used in the navigator are
based on mathematical models. Local deviations in propagation
speed are not included. The calculated positions may therefore
differ from positions obtained by dedicated Decca receivers by
several hundred meters.
DEFAULT
A condition that the navigator assumes automatically if no other
condition is initiated by the operator.
DEVIATION (COMPASS)
Magnetic compass reading error due to local magnetic field
influences.
DGPS
See DIFFERENTIAL GPS.
DIFFERENTIAL GPS (DGPS)
A method of refining GPS position solution accuracy by
modifying the locally computed position solution with correc-
tion signals from an external reference GPS receiver (monitor).
DILUTION OF PRECISION (DOP)
Version 3.3
Operator's Manual
199