Parallel Sailing - D.Long from Departure

Parallel-sailing conversion: difference of longitude (D.Long) from departure and latitude - applies when course is east-west.

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This calculator requires JavaScript to compute its result. The formula, symbols, and regulatory sources are shown in the Formula section below.

Formula, assumptions, and limits

\Delta\lambda = p \sec \phi

Symbol	Meaning	Unit
$p$	Departure	nm
$\phi$	Mean latitude	deg

Source: Bowditch Pub.9 Ch.24

Parallel-sailing conversion: difference of longitude (D.