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    Re: Dip uncertainty
    From: Fred Hebard
    Date: 2004 Dec 6, 22:56 -0500

    On Dec 6, 2004, at 7:24 PM, Frank Reed wrote:
    > Theory aside, I've got some evidence to throw at this problem. I used
    > to live in a twelfth floor apartment within sight of Lake Michigan,
    > roughly 120 feet above the lake level. It's a big lake, so there is
    > still a true horizon even at that altitude. There were a number of
    > other buildings closer to the lake partially blocking the view. One in
    > particular, about half a mile away had a line of stonework aligned
    > with the lake horizon as seen from my vantage point. But it was only
    > aligned on average. I would look at it through binoculars (whenever
    > there was a big freighter out on the horizon). Purely for my own
    > entertainment, I calculated how much the horizon was moving up and
    > down. It was frequently a minute of arc out of line with the average
    > and occasionally 2 and 3 minutes of arc. I made no attempt to record
    > weather conditions or anything like that. It was just fun to see the
    > horizon shifting around from one day to the next. So at that height,
    > there IS real variability in observed dip.
    > Frank R
    > [ ] Mystic, Connecticut
    > [X] Chicago, Illinois
    Sorry, but how were you measuring the difference?

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