The American practical navigator : being an epitome of navigation and nautical astronomy (1888)
Bowditch, Nathaniel, 1773-1838, United States. Navy Dept. Bureau of Navigation, Cooper, Philip Henry, 1844-1912 · Washington : Govt. Print. Off. · leaf 219
Revolvethe micrometer head in theopposite direction until tlietwo images cross each otherand their opposite edges are in contact; read the scale and micrometer head and note the reading. The mean of these two readings (tliat is, half their sum) is the zero reading. Examples. The reading greater… … zero reading would be 2527+1473 = 2000. In another instrument the readings may be 2523 and 1471; then the zero reading would be 2523+1471 : 1997. In measuring angles, it is convenient to apply the difference between the zero reading and 2000 to all readings,calling it the index correction. If the…
Navigation · Nautical astronomy
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