how to make live update of cells?

Hi,
Sorry if the title is misleading, i am not good at making titles

Problem: I have a data validation list in couple cells and would like the index of the item in that list displayed in the cell right beside it using =MATCH(H12,CableList,0).
Note: CableList is the array to look for the H12 value.
Right now, I have to go to that cell, and run that formula again.
I would like to make it so that the index changes as soon as a new item is selected.

I had it the way i wanted a week ago, but it seems i messed up something.
Could anyone please help me solve this problem?

Thanks