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    Re: Ratiometer
    From: Michael Dorl
    Date: 2011 Feb 09, 07:57 -0600

    On 2/8/2011 8:51 PM, Gary LaPook wrote:
    > This guy purchased a "ratiometer" can any of you figure out what it is?
    > http://www.chaski.org/homemachinist/viewtopic.php?f=15&t=89030
    > gl
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    Well, it could be used to compute horizontal distances given line of
    sight distances taken at some angle to the horizontal.  For example in
    rough surveying using stadia distance measurements.
    Also as I remember my surveying class some 55 yrs ago, there was a
    tedious method for computing the area enclosed by a polygon involving
    what were called Latiudes and  Departures, the length of projections of
    a polygon side on the X and Y axis.  The ratiometer could certainly help
    with that given the bearings of the sides.
    Say a segment ran at a bearing of 30 degrees and was 455 feet long.  You
    set the movable arm to the requisite angle, move the slide so that
    touches .455 on the arm, and read off the latitude and departure on the
    scales.  No multiplication needed.  All you have to do is keep track of
    the decimal point but engineers in the slide rule era were good at that.
    But neither of these explains the needle points. :-(
    Quite a collection the fellow has!

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