How to Convert Arc to Time Using The Nautical Almanac
In the following example, you will learn how to convert arc to time using
a table from The Nautical Almanac.
Example: Suppose your DR longitude is 142° 41' W, and ZT is 06h 21m
09s. Divide 142° 41' by 15, and you find that your ZD is +10. This
means that your standard meridian must be 150°W. To simplify the
arithmetic, express the 150°W longitude as 149° 60' W. The values are
equal and subtraction is made easier this way.
Standard time meridian
Longitude your meridian
Difference of Longitude
Using the conversion of arc to time excerpt shown in figure 5-4, change
7° 19' to time, and you get 00h 29m 16s. This means that LMT at your
meridian differs from ZT by 00h 29m 16s.
Figure 5-4. Excerpt from The Nautical Almanac.