So I say "new", but I've been out of the loop for a little bit.
I used to use a third party app called "Pokegenie" to appraise my Pokemon. This would give me a rough guide on how good the Pokemon is based on their overall CP (and other values). Sometimes it would be a range, like 10-15, as well as a list of potential IV combinations, until I leveled them up high enough to give a specific IV.
However now the new in-game Appraisal system evaluates the IVs. The Pokegenie app now says that it can give a specific report on what the IVs actually are, based on this Appraisal.
So how accurate are these Appraisals? Do they give the actual IVs, or is it an average IV based on their current range?
For example, if one IV is 5-15, the average would be 10, but the actual IV might be 12, once they level up.
Best Answer
The new appraisal system shows the exact IV's of your Pokemon:
each chunk represents 5 IV's. If the bar is empty, it's 0 IV, if it's full and a darker red colour, it's 15.
I don't use the Pokegenie app but I assume it's just looking at how full the bar is and telling you the exact IV as it can be a little tricky to tell at first just by eyeballing it.
For example, it's obvious when it's 10 or 15 IV's, as the bar's filled up right to the end of a chunk; but when it's 11 or 12 it might be a little hard to tell the difference at first. But after a little practice, I personally don't think an app is necessary to tell you what IV's your Pokemon has anymore.