An additional bearing, using a charted object other than those used to fix the position, observed and plotted in order to insure that the fix is not the result of a blunder

Related Terms

TREENAIL

A long wooden pin used to fix planks of ship to the timbers

CELESTIAL FIX

A fix established by means of two or more celestial bodies

CIRCULAR FIX

The designation of any one of the erroneous fix positions obtained with a revolver or swinger

DOUBLING THE ANGLE ON THE BOW

A method of obtaining a running fix by measuring the distance a vessel travels on a steady course while the relative bearing (right or left) of a fixed object doubles. The distance from the object at the time of the second bearing is equal to the run between bearings, neglecting drift.

ESTIMATED POSITION

The most probable position of a craft determined from incomplete data or data of questionable accuracy. Such a position might be determined by applying a correction to the dead reckoning position, as for estimated current; by plotting a line of soundings; or by plotting lines of position of questionable accuracy. If no better information is available, a dead reckoning position is an estimated position, but the expression estimated position is not customarily used in this case. The distinction between an estimated position and a fix or running fix is a matter of judgment.

ERROR ELLIPSE

The contour of equal probability density centered on the intersection of two straight lines of position which results from the one-dimensional normal error distribution associated with each line. For the 50 percent error ellipse, there is a 50 percent probability that a fix will lie within such ellipse. If the angle of cut i

FIX

A position determined without reference to any former position; the common intersection of two or more lines of position obtained from simultaneous observations. Fixes obtained from electronic systems are ofte

OUTSIDE FIX

A term describing the fix position determined by the method of bisectors when the lines of position result from observations of objects or celestial bodies lying within a 180° arc of the horizon.

RUNNING FIX

A position determined by crossing lines of position obtained at different times and advanced or retired to a common time. However in celestial navigation or when using long-range electronic aids, a position determined by crossing lines of position obtained within a few minutes is considered a FIX; the expression RUNNING FIX is applied to a position determined by advancing or retiring a line over a considerable period of time. There is no sharp dividing line between a fix and a running fix in this case.

SELECTIVE AVAILABILITY

A Department of Defense program which degrades the accuracy of the pseudorange measurement of the GPS signal by dithering the clock time and ephemerides data, providing a less accurate fix for civilian users. It can be turned on or off at will by DoD.

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