Re: A question regarding timing

From: Mike Waterman (Mike.Waterman@marconi.com)
Date: Wed Feb 14 2001 - 00:55:52 PST

  • Next message: Rush Austin: "Re: A question regarding timing"

    Accurate timing normally comes in 2 parts:
    (a) An accurate time reference
    (b) Accurately timing the difference between the reference and 
    the satellite event.
    
    Traditionally stopwatches have been used for (b). I staryted with
    mechanical stopwatches, later electronic, for a while used a wristwatch
    with stopwatch action (rather fiddly in the dark). Make sure the stopwatch
    can time several events from the same reference time.
    
    For the time reference, most observers use radio time signals. In the
    UK (and probably some other countries) there are telephone time signals
    (the UK give 3 pips each 10 seconds, and are accurate to at least
    0.1sec).
    
    Leo Barhorst and others use a clock permanently synchronised to
    a radio time signal, which simplifies things.
    
    I use an electronic clock connected to a computer, and a pushbutton
    connected to the computer. I just press the button, and the computer
    measures the time from the last 1-second clock tick to the press, giving
    the true time directly in the computer. This saves errors in reading
    stopwatches and typing in the times. You may have noticed some recent 
    seesat postings about misread stopwatches and wrong time zones.
    I calibrate the clock with radio time signals.
    
    I have used a PC's internal clock(s), but 
    (1) they are not so accurate
    (2) the clock you read when the computer is on is different to
    the battery-powered clock that keeps going when the PC is off;
    and so deviates at a different rate from UT. This can be allowed
    for.
    Does anyone know how to read the battery-powered clock directly?  
    
    In emergency (or observing away from home) I go back to mechanical
    stopwatches: they are still working after my electronic ones have
    failed.
    
    Mike Waterman      mike.waterman@marconi.com
    
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