Formula/macro - Apply certain formula as per duplicate cells in column L

I finally have had time to continue with my macros. God bless for weekends!
JBeaucaire, you actually did solve it! Brilliant!!!!!

Values in AF are supposed to change. Same goes with with AE. This was presented in the example though I did not mention it in explanations.
Note how values in AE and AF and change.

Before
-------------- ------------L ------------------- --AB-- ---------------AC ---------------AD ---------------AE ----------------AF
Row 2---- L57951111111 ------------ empty ---------------- 0 ---------------- 0 ----------------- 0 ----------------- 0
Row 3---- L57951111111 ------------ empty ---------------- 0 ---------------- 5 ---------------- -2 ----------------- 3
Row 4---- L57951111111 ------------ empty ---------------- 0 ---------------- 0 ---------------- -2 ---------------- -2
Row 5---- L57951111111 ------------ empty ---------------- 0 ---------------- 0 ---------------- -2 ---------------- -2
Row 6---- L57951111111 ------------ empty ---------------- 0 ---------------- 5 ----------------- 0 ----------------- 5
Row 7---- L57951111111 ------------ empty ---------------- 0 ---------------- 0 ---------------- -2 ---------------- -2



After
-------------- ----------L ------------------ AB ---------------AC ---------------AD ----------------AE ----------------AF
Row 2---- L57951111111 ------------ 0 ---------------- 0 ---------------- 0 ------------------ 0 ----------------- 0
Row 3---- L57951111111 ------------ 0 ---------------- 0 ---------------- 5 ----------------- -2 ----------------- 3
Row 4---- L57951111111 ------------ 3 ---------------- 0 ---------------- 0 ------------------ 1 ----------------- 1
Row 5---- L57951111111 ------------ 1 ---------------- 0 ---------------- 0 ----------------- -1 ---------------- -1
Row 6---- L57951111111 ----------- -1 ---------------- 0 ---------------- 5 ----------------- -1 ----------------- 4
Row 7---- L57951111111 ------------ 4 ---------------- 0 ---------------- 0 ------------------ 2 ----------------- 2

The real information that I am after is in AE. I just needed a formula to go into AB to complete it. And you formula works like charm. See attached spreadsheet where your formula produces exactly the result required on as per sheet "after",


Could you be so kind and break the formula down and explain me in simple English how it works or what it does.
Can talk me through step by step with LOOKUP(2,1/($L1:$L$1=$L2),$AF$1:$AF1)

I just want to learn this technique for future references.


Thank you for the formula.
Amazing stuff