FB, you write 'Slack is slack so as long as there's some slack at the tightest place.' This has been my thinking. If there is always some slack, however small, there is never really any tension. So why would it matter to add lots of slack rather than to just allow the minimum necessary? That's a mostly rhetorical question, at least for you. But in this thread I have been getting, or interpreting, conflicting messages.

1/16 of an inch of sag is very impressive. I don't try to go near that, though I do use high-end, NJS-certified cranks and rings and bottom brackets in an effort to keep things as concentric as possible.

At risk of taking this too long, I'll add one more thing from my fixed-gear chain experience. After being brought to just the right adjustment of slack, a new chain on the first ride away from home and over gravel sometimes actually begins to feel more taut. But the forward pull on the cog should be able to bring only the opposite. I wonder if particles getting between the chain parts take up the slack. Whatever the cause, I stop, get off and move the wheel forward a touch.

There actually seems much ado in the supposedly simple world of the fixed gear. But I love it, and want to get it right.

Thanks again.