No subject

quickly computed with one second accuracy simply by
calling (time-of-day).  (But it will be off by one
second for each time the implementation fails to
non-count a leap second.)

The time interval between two events while the program
is running is:

(let ((start (tick-count)))
  (wait)
  (/ (- (tick-count) start) (ticks-per-second)))

and a sub-second timer that survives re-boots and
agrees on several computers can be computed from the
epoch-of-zero-ticks.

(+ epoch-of-zero-ticks
   (/ (tick-count) (ticks-per-second)))

Iff an uncounted leap second has intervened
between the epoch-of-zero-ticks and the
time the tick-count was taken then this
number will differ by more than one
from the (time-of-day).

That is appropriate, because the time of
day can not be used to compute exact
time intervals without knowledge of the
leap seconds.

  -- Keith

PS: maybe the tick-count should be made
a real number of seconds and renamed,
getting rid of ticks-per-second.

http://www.ucolick.org/~sla/leapsecs/timescales.html
http://www.ucolick.org/~sla/leapsecs/onlinebib.html#POSIX
http://en.wikipedia.org/wiki/Unix_time

An account of bugs from messing up leap seconds:
http://www.maa.org/mathland/mathland_7_21.html