American practical navigator: an epitome of navigation and nautical astronomy (1914)
Bowditch, Nathaniel, 1773-1838, Logan, George Wood, 1868-1915, United States. Navy Dept. Bureau of Equipment · Washington, Govt. Print. Off · leaf 199
rc of exactly 180°,for the purpose of adjusting the line of collimation. On top of the rule near its centeris the level—sometimes replaced by two levels at right angles—by means of which itmay be seen when the table is in a true horizontal position. A magnetic needle mounted in a rectangular metal… … FIG. 63. 4:13. To be hi correct adjustment, a plane table must comply with the followingconditions: (a) The fiducial edge of the rule must be perfectly straight. (6) The level musthave the bubble in its central position when the table is truly horizontal, (c) Thevertical cross hair must be…
Navigation · Nautical astronomy
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