Like EVE, Dust 514 also has Stacking Penalties for equipping more than one module of the same kind in your dropsuit or vehicle.
Items to which the stacking penalty applies will have the following message in their description:
|“||"Stacking penalties apply to this module; the effectiveness of each additional module after the first will be reduced".||”|
Stacking Penalty is a feature of Dust (and EvE) where multiple modules effecting the same attribute have diminishing results. The module description will say whether the module has stacking penalty or not, but it's important to understand that the penalty is for the attribute itself, not the module. This means that it doesn't matter if you use 2 differently named modules, or even 2 modules from different category, the penalty will still apply if they both affect the same attribute.
 Stacked Bonus Calculator
The following calculator determines the total bonus that will be given to a single stat based on the percentage increases from each module equipped that affects that stat.
To use it, input the percentage bonus of each module that affects that single stat in, separated by commas, to find the total bonus after stacking penalties are applied. For example, if I wanted to find the total bonus of two 10% bonus modules, I would type in to the calculator
10,10 and it would give me the total bonus, which in this case is 19.56%. If the module subtracts values (ie: Profile Dampening) you must preface it with a negative sign. Example for basic + advanced module, would be written as
Preliminary tests indicated that Dust 514 also uses the same formula as EVE, shown below:
S(n) = 0.5^[((n-1) / 2.22292081) ^2]
n = the nth module added S = stacking effect for this particular module addition
Module bonuses are ordered from highest to lowest, thus giving you the maximum bonus.
Although the damage modifiers have the warning, the use of subsequent modules output the full value of the modules and not a reduced one as expected. This has been confirmed by CCP to be a display bug, and that weapon damage modifiers do have the penalty .