Formula indicators are very powerful:

You can use all kind of indicators (automated/ manual/ formula) in a formula indicator including formula indicators.

So what you can do is something like:

({automated indicator}Number of SLA achieved Incident /{automated indicator}Number of total Incident * 100) = {formula indicator}% of SLA achieved Incident

({automated indicator}Number of SLA achieved Problem /{automated indicator}Number of total Problem * 100) = {formula indicator}% of SLA achieved Problem

({automated indicator}Number of SLA achieved Change /{automated indicator}Number of total Change * 100) = {formula indicator}% of SLA achieved Change

({formula indicator}% of SLA achieved Incident + {formula indicator}% of SLA achieved Problem + {formula indicator}% of SLA achieved Change ) / 3 = {formula indicator} Index of IPC processes