Building a baseline consists of various elements.
Measure and Capture Estimates – Teams should capture their estimates for work prior to commencing work on Product Backlog Items. Estimates may be captured prior or during Sprint Planning.
Measure Delivery Against Planned Work – At the end of the Sprint the team should review the completed work against the planned work. In most cases there will be some variance between planned and actual work. Metrics can be captured each Sprint to build a profile of velocity and throughput, as well as reliability of estimates.
Analyse Delivery – Teams should review delivery, such as in a Sprint Retrospective, to understand the root causes of any factors that resulted in any significant differences between estimate and actual delivery. Both effort and duration should be considered to better understand team velocity and throughput. Additional considerations such as staff unavailability should be taken into account.