The horizontal angle of the region of indefinite characteristic near the boundaries of a sector of a sector light. Also called ARC OF UNCERTAINTY.
Related Terms 
ARC
A flash, caused by an electric current ionizing a gas or vapor.

SPREAD
The divergence of the air stream in a horizontal or vertical plane after it leaves the outlet.

HARMONIC FUNCTION
Any real function that satisfies a certain equation. In its simplest form, as used in tide and tidal current predictions, it is a quantity that varies as the cosine of an angle that increases uniformly with time

GREENWICH HOUR ANGLE
Angular distance west of the Greenwich celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of a point on the celestial sphere, measured westward from the Greenwich celestial meridian throug

GREENWICH HOUR ANGLE
Angular distance west of the Greenwich celestial meridian; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of the Greenwich celestial meridian and the hour circle of a point on the celestial sphere, measured westward from the Greenwich celestial meridian throug

GRID RHUMB LINE
A line making the same oblique angle with all grid meridians. Grid parallels and meridians may be considered special cases of the grid rhumb line.

GRID MAGNETIC ANGLE
Angular difference in direction between grid north and magnetic north. It is measured east or west from grid north. Grid magnetic angle is sometimes called GRID VARIATION or GRIVATION.

GYROSCOPIC DRIFT
The horizontal rotation of the spin axis of a gyroscope about the vertical axis

HORIZONTAL EARTH RATE
The rate at which the spin axis of a gyroscope must be tilted about the horizontal axi

HORIZONTAL DANGER ANGLE
The maximum or minimum angle between two points on a chart, as observed from a vessel, indicating the limit of safe approach to an offlying danger.
