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    Re: Manufacture of Bygraves
    From: Gary LaPook
    Date: 2009 Aug 17, 23:43 +0200

    The MHR1 just sold for 1990 pounds, $3300 US, way out of my price range. 
    I am glad that I got to hold three of them in my hands last month in London.
    
    gl
    
    Brad Morris wrote:
    > http://cgi.ebay.com/U-Boat-MHR-1-Dennert-Pape-Sextant-Calculator-Slide-Rule_W0QQitemZ140338425807
    >
    > currently on eBay.  Looks like a very nice one.
    >
    > For all the talk of the Flat Bygrave (hat's off Gary), there is nothing, 
    absolutely nothing like the feel of this solidly made, top rank instrument.  
    I recommend it highly!
    >
    > Best Regards
    > Brad
    >
    >
    > ________________________________________
    > From: NavList@fer3.com [NavList@fer3.com] On Behalf Of glapook{at}PACBELL.NET [glapook{at}PACBELL.NET]
    > Sent: Wednesday, August 05, 2009 11:19 PM
    > To: NavList@fer3.com
    > Subject: [NavList 9378] Manufacture of Bygraves
    >
    > I was in London last month and made arrangements (with the assistance of 
    Geoffrey Kolbe, thanks again) to see the examples of Bygraves and the HR 
    series held by the Science Museum and by The National Maritime Museum. I 
    attach two photos showing my hot little hand holding examples of each.
    >
    > The Bygrave I saw was a Mk II serial number 105, the same one shown in Van 
    Riet's paper. I measured the diameters of the scales, actually their 
    circumfrances using a tape measure, and my numbers are very slightly 
    different than his. I believe my measurements are accurate to one-half of a 
    millimeter.
    >
    > The circumfrances were:
    >
    > Cotan   174mm
    > Cos     187mm
    > Cursor tube 203mm
    > Knob at bottom of cosine scale  207mm
    >
    > Dividing by Pi gives diameters of:
    >
    > Cotan 55.4mm
    > Cos   59.5mm
    > cursor 64.6mm
    > Knob 65.9mm
    >
    > I am attaching two photos showing two details of the construction. One is a 
    photo of the cotan scale showing that it was printed on paper and then 
    wrapped around the tube. You can see the gap that has developed over time. 
    The second shows a detail of the long pointer, it is bent downward to be near 
    the cotan scale to eliminate parallax.
    >
    > The National maritime Museum has three examples of the HR1 and one example 
    of the larger HR2. The three HR1s were in cans and the HR2 had a cover and 
    was obviously meant to be mounted on a desk. The first two HR1s I examined 
    were in perfect shape but the third one (the one I am holding in the picture) 
    was in poor shape. I am attaching two photos of the HR2 one showing the scale 
    revealing the same construction method used in  the Bygrave, a paper scale 
    glued around a tube.
    >
    > It was a thrill for me to actually see these instruments. My first 
    impression was that they are very big compared to the one I constructed which 
    is only one and a half inches in diameter.
    >
    > gl
    >
    >
    > 
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