Stat modifiers

Like many role playing games, Borderlands is rife with stats, and modifiers.

A stat modifier, for example, is "+50% Damage". While this mechanic is usually pretty straight forward, there are some pitfalls, and some not-so obvious details:

Adding modifiers
When a player/weapon has several different sources of a same modifier, they will combine additively to each other to create a grand total. This total can be either positive or negative.

For example:
 * Damage, for a player
 * +50% Damage from proficiency
 * +100% From MOD
 * +25% From Skill
 * Grand Total: +175% Damage


 * Recoil, for a weapon
 * -50% Recoil from Barel5
 * +20% Recoil from Body2
 * Grand Total: -30% Recoil

Amplifying modifier
Once the grand total is calculated, it is applied as a whole to the corresponding value (and not 1 by 1): Having two +100% Damage modifiers will triple your damage, not quadruple it.

Positive totals
If the total is positive, then it is straight up applied. For example, wielding a 100 damage gun and with a +175% Damage modifier, the gun will deal 100*(1+1.75) = 275 Damage.

Negative totals
When the total is positive, borderlands uses another formula. Instead of straight up applying the modifier, Borderlands applies the opposite inverse. For example, for a with a spread modifier of -130% from a barrel5, the actual modifier will be of 1/(1 + 1.3). If the gun had a base spread of 2, the final spread will actually be of 0.43.

The rationale for this mechanic is to have the same scale of effect, regardless of the modifier's sign.

A notable list of stats that are affected by this rule are:
 * Damage: Many weapon parts actually have negative bonuses.
 * Spread: Very often breaks the -100% bar.
 * Damage reduction: Brick and Lilith's skills.
 * Recoil: Internally, Borderlands uses a "Recoil" stat, which is then inversed and displayed as "Recoil Reduction"

Scope of the modifiers
Modifiers have two scopes: Gun and player. Basically, a gun will have its own internal modifiers, but these are invisible to the outside world. The gun will appear as a "base" to the player. The Player's modifiers will not mix with the gun's modifiers.