Richard,
so, the last link: take the stopwatch example (from a layperson's perspective), I can't see significant difference in overhead between say this and the elapsed timer example but I'm probably missing something? Like, am I correct in concluding there's a awful lot going on for when an interrupt is triggered like saving system variables and whatnot, or as in your stopwatch code, both the timer1 and timer3 interrupts call a PBP subroutine with assembler commands within and because of this, the system variables don't require backup and restoring after each interrupt activation? Apologies for what might be dumb questions, I'm trying to get my head around this.

Troy