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 <email@example.com>
Permission is granted to copy, distribute and/or modify this document under
the terms of the GNU General Public License, Version 2 any
later version published by the Free Software Foundation.
On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-licenses/GPL.