On 1 March your 2135 zone time DR position is LAT 23°54.0' N, LONG 63°22.0' W. At that time, you observe Schedar bearing 328°psc. The chronometer reads 01h 35m 16s, and the chronometer error is 00m 07s slow. The variation is 3.5°E. What is the deviation of the standard compass?
• How to convert a per standard compass (psc) bearing of a star to a true bearing using deviation and variation corrections • Using the chronometer time and error with the Nautical Almanac to find the Greenwich Hour Angle (GHA) and declination of Schedar on 1 March • Comparing the calculated true azimuth of the star from your DR position with the observed compass bearing to deduce deviation
• Start by turning the chronometer reading into correct UTC using the given error, then think about what you would look up in the Nautical Almanac for Schedar at that time • From your DR position, what sight-reduction steps (Hc/Z) would give you the true azimuth (Zn) of Schedar? Once you know the true bearing, how do you relate it to the compass bearing to isolate deviation? • Remember the sign convention: when going from true to compass ("True Virgins Make Dull Companions" or similar memory aid), where does variation fit and where does deviation fit?
• Verify you are using corrected UTC (after applying the 7-second slow error) before taking GHA and declination from the Almanac • Double-check the zone description for your time zone to be sure you have the right UT for 2135 zone time on 1 March • When you compare the calculated true azimuth with the observed compass bearing, be very clear on whether you are solving for deviation east or west, and re-check the sign using a compass-deviation diagram.
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