Real Time-ing

[Taylor Hillegeist via Digitalmars-d-learn]

So, I mostly do programming that is of run to completion verity. 
But I have a dream of calling functions periodically. So my 
question is:

What is the best (most time accurate) way to call a function 
every n time units?
What is the best way to measure the jitter of these calls?


I'm also interested in waiting vs calling periodically eg.

call
wait(1 ms)
call

is not the same as 1 ms from call to call, due to the time 
duration of the function call.

Thanks!