SLAs only measure the last time an issue is stayed in a state. I also need to know how much in total an issue is stayed in a state.
For example suppose we have Start, A, B and Resolved. This is what happened:
Start->A(1)->B(1)->A(2)->B(2)->Resolved
SLA is only calculated for A(2) and B(2) but I also need A(1)+A(2).