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    Re: Longitude by calculator -theodolite
    From: Paul Hirose
    Date: 2013 Jul 01, 22:18 -0700

    Bruce J. Pennino wrote:
    > The stop watch idea is a good one, and I'll look  for one. But I like
    > just reading my digital watch; simple. Someone please recommend a stop
    > watch of the variety described by Paul.  It would make tabulating data
    > easier!
    
    There are so many stopwatches, it would be hard to recommend a specific
    one. Just do a Web search with a few keywords, e.g.,
    
    stopwatch cumulative split memories
    
    The appropriately named stopwatchcentral.com has a large selection.
    Accusplit has a glossary online. I didn't know there was such a thing as
    a WOS (watch operating system)!
    
    http://stopwatchcentral.com/Select-By-Features/Cumulative-Split-Stopwatches.html
    http://www.accusplit.com/StopwatchResources.aspx
    
    There are two kinds of splits: lap and cumulative. The latter is what
    you need. The watch freezes the display but keeps running internally
    without resetting to zero. A "lap split" is similar, but instantaneously
    resets the timer to zero on each split. That's just the thing for taking
    race car lap times. But if you started the watch at a specific UTC, you
    lose the "hack" as soon as you take a split.
    
    Many if not all split action stopwatches let you select either type of
    split. Even my $25 Timex has that option. My old stopwatch - the one
    that quit working - displayed and saved both types of split
    simultaneously. By the way I found that watch today, so caked with dust
    I had to go outside to blow it off. Must be 5 - 6 years since I last
    touched it. The clock is still running, though several minutes off. The
    only thing wrong is that one button doesn't work.
    
    A set of memories to hold several splits is a necessity for observing in
    the dark.
    
    An advantage of a stopwatch over an ordinary watch is that you can hack
    it precisely and with equal ease to a visual or aural time standard.
    When I check my clocks by eye and ear against WWV, I estimate error to
    the nearest 1/4 second. But with a stopwatch I used to take splits on
    WWV ticks and be consistent to plus or minus .02 second.
    
    
    > Because my theodolite body  has a low height (a short pivot, hard to
    > describe), I must select a celestial body at relatively small Hs (large
    > zenith angle). Say it another way, I can't get my eye to instrument if I
    > want to sight a large Hs. My maximum Hs is 30-35 degrees.
    
    Yes, I'm familiar with that problem. I've never owned a right angle
    eyepiece. Apparently they're in demand. Every time one appears on eBay
    it attracts good bids.
    
    > Deflection of the
    > vertical is one of those errors that I just "lump into small errors
    > difficult to quantify".
    
    But deflection of the vertical *is* something you can easily quantify.
    More precisely, the National Geodetic Survey has a online tool for that.
    All you have to do is apply the corrections for xi and eta. With no
    corrections, your theodolite is effectively disleveled by those angles.
    
    --
    I filter out messages with attachments or HTML.
    

       
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