On the IV page, it should mention another option available for HG/SS users (possibly Platinum users as well, I never bothered to get Platinum so I would never know). The Super Nerd/Collector/PokeManiac (I can't determine which overworld is which at the time) that stands next to the PC in Battle Tower of the Battle Frontier. Show him any of your Pokemon, and he will tell you how well your Pokemon's "potential" is. I'm sure there's some complex formula to determine what makes him spout what phrase at this point, but all I can tell is that his answer reflects how high your Pokemon's average IV sum is.
After that, he'll tell you the Pokemon's stat which has the highest IV out of all else. He'll then tell you just how high it is.
From what I have observed, he'll say any of these three statements, each somewhat determining the precise number of IVs. However, this method simply narrows it down.
"It's very good in that regard." - 18-24
"It's fantastic in that regard." - 25-30
"It can't be better in that regard." - 31
There are probably other phrases as well, I just haven't seen him say anything else yet. I found this in HG/SS and have no idea if it is also in Platinum. Another thing to note: if your Pokemon has, say, 31 IVs in two or more stats, I don't know what he will say. He'll probably say that your Pokemon's overall potential is fantastic and pick one out of the 31 IV stats and tell you it can't be better in that regard. Dunno, just guessing at that point here.
ALSO. I haven't seen it anywhere yet, but I'll mention it now. For the Hidden Power page, you should include that there is a short way of solving your Pokemon's Hidden Power type in-game. This only works in HG/SS, from what I've seen.
In the Celadon Game Corner, there is a man in the "Prize House" who will identify any Pokemon's Hidden Power type for you. Just present it to him, and he will tell you up front. This eliminates the need to type in any gigantic formula into a calculator (IV calculator or otherwise) to figure out the type and gives you the type, and therefore the value, of the Pokemon's Hidden Power. It does NOT determine the Hidden Power's base power, but it does allow you to immediately head into the second formula. Plus, it also will help you determine if you used the IV calculator right, because if you did, the type result on the IV calculator will match what the man has told you.
I am certain that I am not the first non-Nintendo employee nor the first person on this forum to notice this, in fact I can assume Serebii has already seen these, but I just think they should be put up as alternatives for some overly tedious formulas.