Need to use Custom field in key figure calculation but i can't due to it's type

[helenmousa]

Hey 

I have a custom Field that hold the PGI date (it's updated from ECC to C4C ). the field was characterized as text in the very beginning and now i can't change it to Date.

i need to calculate the SLA according to this field : PGI date - reported date 

the PGI date is not available for me 

how i can handle that issue ? i will be glad to have any ideas 

thanks in advance 

helen 

[helenmousa]

using a workflow i am catching the PGI field change date in new field in the right type Date that called PGI change date. and now i need this new field to be a key figure so i can use it in my calculation.