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http://www.johngineer.com/blog/?p=648
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http://hackaday.com/2010/03/09/tube-clock-database
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http://www.dutchtronix.com/Arduino-ClockShield.htm
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http://www.edn.com/index.asp?layout=article&articleid=CA46577
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http://www.dutchtronix.com/ScopeClock.htm