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Accurate Clock Pendulums$
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Robert J. Matthys

Print publication date: 2004

Print ISBN-13: 9780198529712

Published to Oxford Scholarship Online: January 2010

DOI: 10.1093/acprof:oso/9780198529712.001.0001

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The Allan variance and the rms time error

The Allan variance and the rms time error

(p.37) Chapter 8 The Allan variance and the rms time error
Accurate Clock Pendulums

Robert James Matthys

Oxford University Press

The traditional plot of a clock's time error versus time is far superior to the Allan variance for showing a pendulum clock's time performance. The Allan variance is admittedly a universal and statistically more accurate measure of a clock or oscillator's random frequency and time variations (that is, variance), because it is averaged over multiples of each time interval. However, it is a whole curve on a graph instead of being just a single memorable number, and its value is drastically reduced by the short time span it is able to cover. The variance, however, can be used to generate an oscillator's ‘root mean square (rms) time error versus time’ curve, a curve that is much easier to understand. But the rms time error's equally short time span also drastically limits its value to the clockmaker.

Keywords:   Allan variance, time error, pendulum clock, root mean square, time, time performance, time span, oscillator

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