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    Re: How to Use a Plastic Sextant
    From: Frank Reed
    Date: 2011 Jan 14, 23:04 -0800

    Scott, you wrote:
    "I recently received the David Burch book on how to use a plastic sextant, as a gift. This is a unique book with lots of very useful information and instructions about using a sextant, much of which translates very well to the understanding and use of metal sextants also. I know many disparage plastic sextants, but I have no financial tie to the book, and would highly recommend it."

    First, another disclaimer: let's not confuse admitting that plastic sextants are not as good as metal sextants with bashing them completely. Plastic sextants are real sextants, and as David Burch writes in the book, as long as you treat them very gently and with considerable attention to detail, you get very good results. But a good metal sextant (not just any metal sextant) will produce better results and probably with less attention. The choice is largely a matter of price.

    Ok, disclaimer out of the way, I agree completely that this is a very fine book with lots of information that's valuable to both beginning and experienced navigators and navigation enthusiasts. BUY IT. Practically anything you can do with a sextant (apart from opening bottles of beer...) is covered in this book. It's really good. The section on sextant piloting is more detailed than any other treatment that I have seen. There's also a really nice, extensive discussion on using the "slope" method to deal with outliers, which Peter Fogg was also recently describing on NavList.

    The only flaws I've seen in this book are flaws found in practically any book on sextants written in the past fifty years. For example, he refers to "side error" as a "crucial" adjustment, which just isn't true. And indeed by the end of the section, he ends up saying that it "does not really enter into the actual sighting error". Side "error" is no error at all except in certain special situations where it can easily be worked around. He also describes swinging the arc or "rocking the sextant" in a manner which appears to match the limited mid/late 20th century approach that we discussed recently. The section on Bruce Stark's lunar tables, also published now by Starpath, feels very much like an advertisement, but hey, that's how we pay the bills.

    This edition of "How to Use a Plastic Sextant" is hot off the presses. For example, in the references, there is an account of some sights taken by NavList's own Peter Hakel and described on NavList at the end of August, 2010 (see p.83). In fact, there are quite a few names from NavList to be found in this book in addition to Peter's. There's David Burch himself, who is mostly a "lurker" these days. There are Bruce Stark and Peter Ifland, who haven't posted in years, but may still be checking in now and then. Geoffrey Kolbe and Bill Morris are mentioned in the references on p.69. Hewitt Schlereth turns up quite a few times thanks to his work with the Starpath School of Navigation (if I understand correctly) and also his extensive experience with plastic sextants. And yes, even my name turns up a couple of times in reference to lunars.

    I learned one more thing when I got to the biographic section at the back which I don't think I had heard previously. David Burch is yet another physicist. I'm telling you, folks, we physics types are a pox on navigation! ;)

    -FER


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