| 摘要 |
The instrument comprises a sphere mounted in a holder between two rings, so that the sphere is held in specific spatial relationship to holes in the holder which define a line of sight of the instrument. A flat cylindrical assembly comprising a bubble level and a compass is mounted on the sphere with the center of the assembly at a point which represents the point on the earth's surface intersected by a line from the earth's center to the geostationary satellite served by the instrument. The assembly touches and moves between the rings. A mark on this assembly points in the direction of a point on the sphere which represents true North relative to the center of the assembly. A map of the area served by the satellite is marked on the sphere. A scale marked in degrees and having a base point is mounted between the rings with its centerline parallel to the rings. The map is marked with points representing major locations at which antennas may be located. In use the sphere is moved in the holder so that the selected point is under the base point on the scale and then the instrument is positioned so that the north end of the needle points at the mark on the assembly and the bubble is centered in the level. The map is distorted, to account for magnetic and gravitational deviations such that when the above described procedure is followed the line of sight is aimed at the satellite.
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