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    Re: Level of observation accuracy
    From: Dan Allen
    Date: 2004 Jul 24, 12:58 -0700
    I have always wondered if I could make a fairly accurate sextant-like device out of just a heavy weight (plum bob) on the end of a line hanging from something, perhaps another line or a tree.  Anyway, then I could measure with an accurate tape measure the height of the line, measure the length of the shadow, and take some arctangents and get an angle.   If the line and length of shadow are long enough, serious accuracy could be achieved, no?  Anyone done this or see any obvious deficiencies in this inexpensive method?
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM]On Behalf Of Frank Reed
    Sent: Saturday, July 24, 2004 12:29 PM
    Subject: Re: ReRe: Level of observation accuracy

    Bill wrote:
    "While I hate to admit it, started this quest a couple of months ago with
    Celestaire's Wurzburg cardboard sextant.  Manufacturer claims it can be
    accurate to within 8 minutes of an arc.  With a little mirror tweaking and
    putting a horizontal slit across the eye side of the viewing tube, am
    getting within 2-3 minutes consistently from seated position on a stable
    platform or tripod mounted.  So I figure plus/minus 3 minutes is my range of
    instrument slop.  Humidity does affect index error. <G>"

    Very interesting. Cheap sextants are nothing to sneeze at. Most people eventually prefer to get a fancy one simply because they look so professional, but by practical standards plastic and cardboard sextants are very good.

    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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