ABSTRACT
That typical computer clocks behave in ways quite counterproductive to good timekeeping should come as no surprise. For example, in a survey of about 20,000 Internet hosts synchronized by NTP, the median clock oscillator frequency error was 78 ppm, with some oscillators showing errors greater than 500 ppm [1]. With a 78-ppm frequency error, the time error over 1 day accumulates almost 7 s. Commodity computers have no explicit means to control ambient temperature, crystal drive level, voltage regulation, or mechanical stability so the oscillator frequency may vary over a few parts per million, in the normal course of a day.
