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    Re: Whyle Thomson & Co Glasgow
    From: David Pike
    Date: 2016 Jun 12, 02:22 -0700

    A few days ago in a secondhand bookshop I found a copy of AP3270. I did not buy it but  will probably return and add it to my collection

    David  If you’re thinking of buying a SH copy of AP3270 you need to know that it comes in three volumes.  Volumes 1, 2, and 3, or red, green, and yellow bands.  You might not remember the numbers, but you will remember the colours.  The red-band is for selected stars.  The green and yellow bands are for bodies with declinations from 0-29 degrees, mainly the Sun, Moon, and Planets.  The green-band is for latitudes 0-39 degrees, and the yellow-band is for latitudes 40-89 degrees and of most value in the UK. 

    You also need to know that whereas the green and yellow bands more or less remain current for ever, the red band-has to be epoched because of Precession and Nutation and Stellar Motion.  If you buy a red-band outside its 10 year epoch value, it’s not much use for current practice.  You can spot if the copy in question has come from an aircraft, because it will probably have the aircraft serial number marked on the front.  Chasing that serial alone on the internet can be an interesting couple of hours.

    To calculate sights, you’ll also need GHA Aries for the particular time and date.  This is readily available on-line or from a purchased Nautical Almanac.  If you want 10 minute GHAs, go to the US Air Almanac available free on-line, but there are necessarily a lot of pages to it. 

    Before you spend a lot of money on expensive refurbishment, it might be worth spending around £12 on Bruce Bauer’s The Sextant Handbook: Adjustment, Repair, Use and History.  https://www.amazon.co.uk/Sextant-Handbook-Adjustment-Repair-History/dp/0070052190 .  It might well save you a lot more cash in the long run.  DaveP

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