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    HO218/AP1618 – A useful little boo k
    From: David Pike
    Date: 2015 Nov 5, 03:49 -0800

    It’s amazing how when researching one thing you find an answer to something else you can’t remember if you actually heard in the dim and distant past or just dreamt.  Looking at AP1618/HO218 has confirmed such a memory.  I said in a recent post http://fer3.com/arc/m2.aspx/Bubble-Sextant-Dip-Meter-DavidPike-oct-2015-g33230 that I believed the D (-10°) position on the RAF MkIX and Periscopic Mk2 sextants could be used to calculate distance-off from distant surface features.  Well AP1618/HO218 confirms this.  Table X gives ranges up to 60nm for depression angles up to 10° for various aircraft heights.  However, the instructions do make the point that the ranges obtained must be treated as approximate.

     Gary.  I was interested to see your P&N correction update table to HO218.  http://fer3.com/arc/img/115971.h.o.-218-correction-table.jpg Which start date was that based upon.  My AP1618 is based upon values for 1940 or 41 and has an update table I going to the year 2000.  If I could get a correction table starting 2000, could I just add the correction from 1940 to 2000 to the values for 2000 to 2015 and use my 1940 AP1618 for fun shooting only (like PLs arriving in the right county)?  DaveP 

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