SLA: what it is, how to define it and how to measure it

What an SLA you can meet should include

1. Severity levels defined with concrete examples, not adjectives. “Critical” has to mean the same thing to the customer and to you.
2. Two separate clocks: first response time and resolution time. Mixing them up is a common cause of disputes.
3. Coverage hours and a holiday calendar. A 4-hour SLA does not mean the same thing 24/7 as it does during business hours.
4. Clock pauses: when the next step depends on the customer, the clock stops. If it is not written down, it does not exist.
5. How it is measured and who provides the data. If you measure it yourself in a spreadsheet, the customer has every right not to believe it.