Let Me See If I Understand Recaps...

I start out on, say, a Wednesday and drive 8 hours. I continue though the week until I come to Tuesday. Let's say I've logged 68 hours in 7 days. That means I have 2 hours left. The following Wednesday I gain back the 8 hours I drove on the Wednesday I started out plus the 2 hours I had left over = 10 hours available. Correct?

And, this is driving time, not total On Duty time?

Also, if I've logged 70 hours by the time 7 days are up, I'm not allowed to recap - I have to take a 34-hour rest?

You're close.

The 70hr clock isn't for the week, it's for 8 days. You can't drive if you've hit 70hrs in an 8 day period. So in your example, you wouldn't recap those 8 hours until the 9th day, or Friday.

Any hours recapped, as well as any leftover hours, are On-duty hours, not just driving.

You never have to reset with a 34. But you won't be able to drive again until you get some hours back, either by recapping or resetting. Sometimes it's best just to go ahead and sit for that 34. I would often be near 70hrs by day 6 or 7, allowing me the luxury of enjoying a 34 to get out and explore.