Introduced in Secrets of Faydwer were are series of gem based augments which scale based on what type of item they are inserted into. Because of the complexity of this scaling system it is useful to have small mystical calculator which will do the work for you. Luck for you Alcon the Magnificent scribed such a thing long ago.
Things to note about how Secrets of Faydwer jewelcrafting works - There are two main types of craftable gem augments. There are Type 10 and Type 11. The type 10 augs are based off of simple vendor purchasable gems and add very basic core stats (HP/Mana/Endurance/Str/Dex/Agi/Wis/Int/Cha and saves. The type 11 augs are the stronger augments and can add some good spell effects as well as core stats and heroic stats. The trick is to mix and match and realized that these are all RECOMMENDED not required level items. This means that you can have a level 1 character with a Faruene enabled item and heroic strength.
The other thing to note is that you can only have 1 of a specific type 10 gem in an item. This means that you can not for example put two 150 hp gems in the same bracelet, but you can put a 150hp and a 150 mana/endurance one in.
The other thing to note is that these augs ONLY work in jewelcrafted items (like the dwerium rings, earrings, wrists) and DO NOT work in Cultural smithed armor. So you while an elaborate daybreak wrist might have a Type 11 aug slot, if you put the gem in it won't do anything when equiped.
Never the less these are useful items for filling out certain slots or giving your alts a decent item that can be tuned to their needs. Oh and the cost to remove gems....is almost nothing. Get your glue solvent from the Jewelcraft merchant in PoK or any starting city. It will set you back 1 plat.