As you mentioned the SLA metris, here I&#12288;share my experience in SLA.
Step 1:Confirm the purpose of SLA
Step 2:in my company, we want to know the SLA of customer, we use field MR resovling rate as major .
Step 3:Calulator formula of monitor SLA.
Step 4:established the metrics,
Step 5:Monitor it KPI
Step 6:compare with it find the root cause to change your organization.
First you need to define what to measure (Service) within your process
Second, you need to come up on how to measure you servicers, identify the upper limits (UL) and lower limits (LL) of your thresh holds (Level)
Lastly agreed who the establish standards and monitor or measure the process (Agreement)