What steps will reproduce the problem?
1. Unequip all gear (hp values are too high with all gear equiped to get an accurate reading).
2. Equip piece of gear in question
3. Hit Points gained do not match Hit Points listed by Rating Buster

What is the expected output? What do you see instead?
I would expect the Hit Points to match (or at least be fairly close), instead I see a wide gap in the estimate - Rating Buster stating 1072 HP and the item is giving 1140 HP.

What version of the product are you using?
1.4.2

Do you have an error log of what happened?
No

Please provide any additional information below.
I ran some math with Talents.  Bear form gives a 25% boost to stamina.  Heart of the Wild (talent) gives 20% boost to Stamina.  Survival of the Fittest gives a 6% boost to all stats (including stamina).  If my math is correct, Rating Buster simply adds these to get a 51% gain in Stamina, whereas the game seems to take the Stamina and multiply it by 125%, then take the result and multiply it by 120%, then take the result again and multiply it by 106% ... this would explain the difference.

For instance, for said item mentioned above.  The item has 71 Stamina.

Rating Buster calculates it as 71 * 1.51 = 107.21  then 107.21 * 10 = 1072 HP

The game seems to calulate it as follows:
71 * 1.25 * 1.2 * 1.06 = 112.89  then  112.89 * 10 = 1129 HP (very close to the 1130)

I hope this makes sense.