Final answer:
A service agreement must be in place before customer or Service Provider usage can be calculated, serving as a contract that specifies service levels, costs, and usage terms.
Step-by-step explanation:
A service agreement must exist before a customer or Service Provider (SP) usage can be calculated. This agreement is essentially a contract that defines the terms under which services will be provided to the customer by the service provider. It includes details about service levels, costs, and usage limits. For instance, in a telecommunications service agreement, it might specify the amount of data or number of minutes included in the plan and the rates for any overage.
In the context of information technology, such an agreement is often called a Service Level Agreement (SLA). It assures the customer of a certain minimum level of service and outlines the metrics by which service is measured, as well as any penalties or remedies for service failures.