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    Re: (no subject)
    From: Jim Hickey
    Date: 2006 May 14, 09:36 -0400
    I have enocuntered a situation similar to yours i.e. I did not know an accurate elevation for dip.
    Since I knew the lat and long of where I was, I simply used this lat and long as my assumed position, which should yield a difference between Ho and Hc of 0' if I have done my sights carefully. Any difference I attributed to a value for dip.
    Repeat this a few times and you can determine a pretty good value.
    -----Original Message-----
    From: Roger Puttman <rkputty@WESTNET.COM.AU>
    Sent: Sun, 14 May 2006 18:41:02 +0800
    Subject: (no subject)

    I'm brand new to this site so thanks for having me! 
    As a bit of an amateur I am keen to learn the more basic aspects of astro navigation. I was lucky enough to serve as an assistant officer of the watch on a Frigate and although I didn't get my ocean nav ticket (a long story how I came to be there etc etc) I did get a good grounding in astro. I recently bought a Hezzanith vernier sextant from e bay and I have a couple of nav manuals, (1784 Mariners Compass Rectified and 1842 Navigation by Raper and some modern ones too!) the second is a complete course in the subject, starting at how to do the maths and moving on to the instruments and tables for 1842 to 1845. 
    The first question I have is: I live on a hill overlooking the ocean but dont know my elevation to set the dip. Given I know where I am and can see some islands offshore is there a way I can determine my altitude? I have a chart and can accurately place my house and the islands so there must be a way....I just cant figure it out. I can get off my bum and go down the beach and take sights but it is kind of fun to be able to do it from the backyard... 
    Secondly, a number of you managed to extract Margetts tables from a site but it seems to have been shut down. Is there anyway we can still get access to that site? It sounds excellent for a whole pile of stuff so it is a shame we get it now. As an aside, there was comment on whether Margetts would have been used contemporaneously. I found this from Mathew Flinders which given his abilty as a navigator might be indicative: 
     I am not able to give you precise information of the books and instruments you wish to purchase, but think they may come to near £80 sterling. I do not know much of Heather's charts: we reckon those of Arrowsmith of Faden to be the best. Of the use of Margetts' tables I have no great opinion, but Mendoza's are excellent. I would recommend you to apply to Mottley, bookseller in High Street Portsmouth for both books, charts, and instruments; believing that he will procure for you what may not be kept in the shop; but I rather think you will not stay long enough to receive what may be required from London. 
    Matthew Flinders - Private letter books, Nov. 1810 - May 1814 (Vol. 3) 
     To Mr Antony Roux, Sept. 26, 1811 
    Roger Puttman 
    32.46 S 115.75 E (decimal lat and long, my god what a dogs breakfast) 
    > T= 
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