
This article has a calculator here.

Absorbative is an Invention perk that gives a 20% (22% on a level 20 item) chance of reducing damage by 5% per rank. It can be created in armour gizmos.
Absorbative effectively provides a 1% damage reduction per rank. However, Absorbative does not reduce hard typeless damage (typeless damage that is unaffected by defensive abilities).
Rank

Reduction per hit

Average damage reduction

1 
5% 
1% (1.1%)

2 
10% 
2% (2.2%)

3 
15% 
3% (3.3%)

 All numbers in parentheses refer to level 20 gear.
 The average ratio of damage taken, $r_{avg}$, from Absorbative to that of without Absorbative is
 $r_{avg}={\frac {\sum \limits _{n=0}^{\infty }\left(1p\right)^{n}p\left[\left(\sum \limits _{i=1}^{n}d_{n,i}^{(0)}\right)+\lfloor {\left(1.05\times R\right)\times d_{n}^{(1)}}\rfloor \right]}{\sum \limits _{n=0}^{\infty }\left(1p\right)^{n}p\left[\left(\sum \limits _{i=1}^{n}d_{n,i}^{(0)}\right)+d_{n}^{(1)}\right]}}$
 The average damage reduction is then, after some rearranging,
 $1r_{avg}={\frac {\sum \limits _{n=0}^{\infty }\left(1p\right)^{n}p\left[d_{n}^{(1)}\lfloor {\left(1.05\times R\right)\times d_{n}^{(1)}}\rfloor \right]}{\sum \limits _{n=0}^{\infty }\left(1p\right)^{n}p\left[\left(\sum \limits _{i=1}^{n}d_{n,i}^{(0)}\right)+d_{n}^{(1)}\right]}}$
 Notes
 A calculator for this is at the top of this page.
 Assumption :
 The enemy is dealing damage with anything that is not hard typeless.
 $R$ is the rank of the Absorbative perk.
 $p$ is the proc chance of Absorbative to activate (.2 normally, .22 if the Absorbative perk is on level 20 gear).
 $\textstyle \sum _{n=0}^{\infty }\left(1p\right)^{n}p=1$ when $0\leq p<1$ or $\left1p\right<1$. This represents summing over all possibilities where integer $n\in [0,\infty )$ represents the amount of hits prior to the proc of Absorbative. The probability of Absorbative proccing on hit ${n+1}$ is therefore $\left(1p\right)^{n}p$.
 $d_{n,i}^{(j)}$ is the $i^{th}$ random value uniformly sampled between the enemy's minimum hit and maximum hit. The $j$ describes different sets of hits. The sets are regenerated for every new value of $n$.
 $d_{n,i}^{(0)}$ has $n$ elements with integer $i\in [1,n]$. This is the damage taken before the perk procs.
 Clarification : This does mean that for $n=0$ that there are no elements in this set.
 $d_{n}^{(1)}$ is the damage taken from a single hit when Absorbative procs.
 The set of values in $d_{n}^{(j)}$ for integer $j\in [0,1]$ is the same in both the numerator and denominator of the ratios for any given $n$.
 Simplifications
 This can be simplified if the assumption is that every value $d_{n,i}^{(0)}$ $\forall$ integer $i\in [1,n]$, $d_{n}^{(1)}$ $\forall$ integer $n\in [0,\infty )$ is taken to be the same $\left(d_{n,i}^{(0)}=d_{n}^{(1)}\rightarrow d\right)$. In this scenario, there is no random element and the above $r_{avg}$ is then only dependent on the proc chance. This simplification is increasingly accurate in the limit of large $d$. A table is provided at the top of the page.
Using these simplifications, the damage reduction reduces to
 $1r_{avg}={\frac {pR}{20}}$
Gizmo layout 
Possible perks 







