I have tried various apps in Android or Web-based to calculate the IV of my catches, and at the end I have taken Calcy IV as the most suitable for being a third party quiet easy to use and without any danger to be banned. It takes a screen-capture and makes an OCR of the texts, so it has no contact with the PoGo databases.
Well, I had changed all the names of my Monsters adding the % of IV, so I could easily ponderate which one has to go to the Profesor in order to gain space. The result where names like 96Arbok or 67Mr.Mime.
With time I have noticed that this ponderation isn't enough, so I made tries with the naming function of Calcy IV, and the most suitable for me was the following: 83Blbsr⑫⑩⑭♂ (83% IV Bulbasaur 12 Attack 10 Defense 14 Stamina Masculine)
Well, there started the problem. When I took the decision to change the name-format I see that there was a actualization for Calcy and I took it.
But what surprise, when I used it to change the first to the new name, I had the strange feeling that the IV had changed.
And up to now I was shure to have understand that the IV is something unique, stable, and doesn't change by no meaning. I made more changes, now writing down the old IV, and really it changed, not in all monsters, but in a lot of them, and allways downwards, never upwards.
To see which result is more exact, I have tried to get the results of two web-based calculators (pokeassistant.com and pokemon.gameinfo.io), and both show equal results. The old (81%) and the new (73%) result of Calcy is inside the range both webs show (69 to 93%), but still not even the average of the web (78.2%) is equal. And the combination given by Calcy (12,9,11) isn't inside of all combinations given by the webs... Who is correct?
Details: In the meanwhile I have NOT changed Player-level, I'm still 28.
The only monsters where I have used Candies to level-up are my three 100% Monsters and in two 10 CP, because I wanted to see where they go with their range of 0 to 100 % IV.
Apart of all these things, I have noticed a flaw which I could change manually. Calcy searches for all combinations of IV for the individual values of this monster, but this list can be long. If you use the ingame-valuation of the profesor you can know which of the IV's is the highest. If you mark this specific IV in Calcy, it reduces the range and makes the result more exact.