In memory of the Brown Wood Owl Multi-Cache

Here the  Brown Wood Owl stood for several years.

Suddenly it was gone... https://coord.info/GC4YH1Y

Here's the task you need to solve:
There are 9 letters on the sign.

You should use the letter value in the formula below.
If you put the 6 straight digits into Certitude, you will also get a clue.
 

Good luck!

N 58° 58.abc E 011° 08.def

a = letter # 1 - 13

b = letter # 2 - 13

c = letter # 3 - 2

d = letter # 4 - 15

e = letter # 5 + 5

f = letter # 6 - 19

You can validate your puzzle solution with certitude.