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Sound card clock accuracy

I'm trying to measure the accuracy of sound card clocks running under
Linux and would like to discuss with people on the list about a posible
method of measurement.

An indirect measurement I am using is to sample /dev/dsp at 8 kHz
1,000,000 times and compare time stamps (with millisecond resolution --
ftime()) taken before and after the samplings. 1 million samples at 8 kHz
should take exactly 125 seconds. I am measuring how off from 125 seconds 1
million samples takes and from the difference I calculate the relative
clock error. I am relying on the Linux system clock, so there will be some
additional error, but it should not interfere much with the measurement.

Does any one see a problem with the way the measurement is being 
performed? Any suggestion for improvements?


-- Edson, 7n4ncl