Stacking penalties

Formula

S(n) = stacking penalty for the n:th module
S(n) = 0.5^[((n-1) / 2.22292081) ^2]
or, equivalently,
S(n) = 2^(-0.20237274238855663*(n-1)^2)

n	S(n)
1	1
2	0.86912
3	0.570583
4	0.282955
5	0.105993
6	0.0299912
7	0.00641018
8	0.00103492

Specific cases

m1 = first module
m2 = second module
mn = n:th module
They must be ordered: m1 > m2 > ... > mn
value = the value of the stat being modified

Damage = (1 + m1*S(1)) * ... * (1 + mn*S(n)) * value

ROF = (1-m1*S(1)) * (1-m2*S(2)) * ... * (1-mn*S(n)) * value

Harderners:
Resistance = 1 - (1-m1*S(1)) * (1-m2*S(2)) * ... * (1-mn*S(n)) * (1 - value)
Harderners modifiy not the resistance, but the amount of damage let through.