It reads 8192 bytes from the zaptel timer device (/dev/zap/pseudo). This should take exactly 8000 ms . It uses calls to gettimeofday(2) before and after that read to check that indeed exactly 8000ms have passed.
Values of 100% and 99.99% Are normally considered a definite pass. Values of 99.98% and 99.97% are probably OK as well.
This manual page was written by Tzafrir Cohen <firstname.lastname@example.org>
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