Also Steve, just like Edelbrock says. as you get closer to the optimal tune, the vacuum reading will continue to climb. So that's one other way to tell your heading in the right direction. But again, that's not set in stone, yet, because your timing may not be optimal for the tune yet. I don't know what method you've been using to adjust the idle air screws, but here's how I do it.
If it's an auto, I adjust IN gear with the wheels blocked and parking on. Don't wanna run anybody over. With the engine up to temp and your vacuum gauge hooked to a manifold vacuum source, I adjust them 1/4 turn IN (lean) at the time, until the vacuum on the gauge begins to drop and the engine starts to stumble. Next, I adjust OUT (rich) 1/4 turn at a time until I reach the highest reading on the vacuum gauge. The engine will smooth out once that highest reading is met. Rinse and repeat for the other screw. Opinions vary, but I prefer to make this adjustment with the idle "a little" lower then normal, because you can hear the differences in the way the engine runs and normally see the differences on the vacuum gauge easier, too. Not necessary, but it can help if you haven't done it enough to get used to hearing how the engine responds. If the idle is normal, say about 750, sometimes it will "cover up" so to speak the differences you need to be listening for while making those adjustments.....if that makes sense.