# Celestial USCG exam: Which Questions use Observed Longitude / whole LHA?

**URL:** <https://forum.gcaptain.com/t/celestial-uscg-exam-which-questions-use-observed-longitude-whole-lha/8879>\
**Category:** Maritime Training & Licensing\
**Created:** [November 7, 2012, 2:19pm UTC](https://forum.gcaptain.com/t/celestial-uscg-exam-which-questions-use-observed-longitude-whole-lha/8879 "2012-11-07T14:19:40Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![whitecloud](https://avatars.discourse-cdn.com/v4/letter/w/a3d4f5/32.png) [@whitecloud](https://forum.gcaptain.com/u/whitecloud)\
**Post date:** [November 7, 2012, 2:19pm UTC](https://forum.gcaptain.com/t/celestial-uscg-exam-which-questions-use-observed-longitude-whole-lha/8879/1 "2012-11-07T14:19:40Z")

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I am dragging myself through a Celestial Nav self-study course for my USCG 500-ton Ocean Masters exam, and wondering how to know which questions requiring Pub 229 use Observed Longitude and a whole degree LHA, and which questions require interpolating your true LHA.

For example, a Computed Altitude & Azimuth of the Sun question requires a whole number LHA to get the coast guard’s answer, but a Gyro Error by Azimuth of the Sun question requires using your exact LHA.

How do I know which LHA to use when?

Thanks!

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**Author:** ![CapMick](https://avatars.discourse-cdn.com/v4/letter/c/f17d59/32.png) [@CapMick](https://forum.gcaptain.com/u/CapMick)\
**Post date:** [February 14, 2013, 2:28pm UTC](https://forum.gcaptain.com/t/celestial-uscg-exam-which-questions-use-observed-longitude-whole-lha/8879/2 "2013-02-14T14:28:23Z")

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It has been a while since I have taught CNav or used 229, but I think all Azimuth problems will require Interpolation, but Observed bodies, (Sun, Moon, Stars) generally do not, unless you have to solve a Circle of Equal Altitude.  
Good luck on your License.  
Cheers  
MBM