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    Re: How Many Chronometers?
    From: Frank Reed
    Date: 2009 May 11, 00:06 -0700

    Jeremy Allen, you wrote:
    "I've used the Stark Lunar tables with good results.  As long as you
    know the hour and a decent DR, you can use the tables to determine GMT
    via Lunars to the accuracy of your shooting ability.  They take a
    while to reduce the sight however."
    
    There is nothing "special" about Bruce's lunar tables except (and this 
    exception is important!) the fact that they were published by him at a time 
    when lunars were almost unknown to practical navigators. He almost 
    single-handedly re-introduced lunars back in the 1990s. Apart from that, the 
    tables offer no particular benefit, though they are certainly very clever. 
    
    From the early 19th century onward, there was a mis-conception among many 
    commentators on navigation proposing that the problem with lunars, and the 
    reason that they were not used more often, was the difficulty of the math. 
    This was reputation, not reality. While there were some poor tables 
    published, any of the common methods available worked very well and did not 
    entail significantly different levels of mathematical skill or effort.
    
    You also asked:
    "What I wonder is what ships did in the age of steam before the age of
    common time ticks (say the early part of the 20th century).  I haven't
    seen any ships with more than 2 chronometers on it, but my shipping
    experience is relatively short.  When I worked with chronometers, we
    kept an error and rate log.  The chronometers were serviced
    periodically and reset at that point. Nothwithstanding the early age
    of chronometers, what was the time solution in a more modern age?
    Does anyone have any data on this?"
    
    Just the things that have already been mentioned. Time balls and other signals 
    in many ports which were frequently provided by synchronizing with a local 
    observatory. Spotting a known headland, even a tiny island, with a known 
    longitude. Speaking other ships was also extremely common. And in the age of 
    radio (in the few years before the official time signals) speaking other 
    ships by radio extended the range of this time-honored method from a few 
    hundred yards to hundreds of miles. "What time is it?" (meaning GMT usually) 
    was such an important and common question that it was assigned a Morse 
    shorthand at a very early date. Gary Lapook told the list back in October of 
    2007 that the signal was "QTR".
    
    But just so we're clear, the real solution was multiple chronometers. The 
    other checks are rarely necessary when you have a set to compare one against 
    the other.
    
    -FER
    
    
    
    
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