Hi!  I have a mystery.  Well, sort of.

The original mystery was that "date; sleep 60; date" on my laptop would
take exactly 60 seconds, and print timestamps 35 seconds apart.

I replaced the laptop's CMOS battery, and this no longer happens.

However, in the process, I started trying to understand the i386 clock code,
and I cannot for the life of me figure out how this is possible.  So far as
I can tell, the system's clock is read only at boot.  At runtime, I can
imagine the system getting regular i8254 interrupts (and thus keeping good
time), or I can imagine problems (making the clock slip).

What I can't figure out is how the kernel can keep flawless time in terms
of the duration of timers (such as sleep), while still having the clock
slip.

-s