Jim it seems like every source you find will give you a different spec for the height of the playing surface. Although only 1/4" different, both of these guys have given you different specs, both from the BCA. I was under the impression there was about a 2" range that was in spec, but I haven't looked it up in a while.
I can tell you though that if the table is set up properly, you should have the frame levelled as close as possible before you put the slate on. If your frame is properly levelled, you should have at least one leg that sits on the floor (with no shims under it). You should start levelling from the high corner and bring the rest of the frame up to level with it. If you've got shims under all 4 legs, you're frame is too high.
As far as the height of the slate once it's installed, it will vary over the length of the table, depending on the slope of the floor and possibly any warp in the frame. That's why there's an acceptable "range" in playing surface height.
I hope this helps. Definitely use Scruffy and Tiddler as a guide, but I wouldn't be too upset if the whole table isn't exactly 30" from the floor. I've seen many tables on floors that sloped MUCH more than a half inch over the length of the table. Even some that needed a 2x4" block under the leg!!!
Good luck.
