Take your DR-Lat and round it up or down to whole degree.
Choose a-Lon° = DR-Lon° and a-Lon' = GHA'
- Look at the difference and call it Delta
- You're done if delta is less than or equal 30'. The AP is a-Lon° a-Lon' = DR-Lon° GHA'
- If Delta is greater than 30', then we need to change a-Lon° by 1° up or down according to step 5 or 6
- Western Longitude: If GHA' is greater than 30' then decrease a-Lon° by 1° and increase it if it's less than 30'
- Eastern Longitude: If GHA' is greater than 30' then increase a-Lon° by 1° and decrease it if it's less than 30'.
a-Lat = Assumed Latitude, a-Log = Assumed Longitude, DR = Dead Reckoning, GHA = Greenwich Hour Angle