A marine sextant accessory consisting of a tubular sighting vane, the function of which is to keep the line of vision parallel to the frame of the instrument when observing horizontal sextant angles.

Related Terms

RESTRICTOR

A device for producing a deliberate pressure drop or resistance in a line by reducing the cross-sectional flow area.

AMMETER

An instrument for measuring the magnitude of electric current flow.

HYDROMETER

An instrument for determining either the specific gravity of a liquid or the API gravity.

SPREAD

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

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.

HAND LEAD

A light sounding lead (7 to 14 pounds), usually having a line of not more than 25 fathoms

GROUND LOG

A device for determining the course and speed over the ground in shallow water consisting of a lead or weight attached to a line. The lead is thrown overboard and allowed to rest on the bottom. The course over ground is indicated by the direction the line tends and the speed by the amount of line paid out in a unit of time.

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

HUNTING

Fluctuation about a mid-point due to instability, as oscillations of the needle of an instrument about the zero point.

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