To measure dev team velocity, you can use the following formula:

Velocity = Total story points completed in a sprint / Number of sprints. Start by estimating the effort required for each task using story points. During the sprint, track the completion of these tasks and sum up the total story points completed. At the end of the sprint, divide this total by the number of sprints to get the average velocity.

Another method is to use burn-down charts to visualize the progress of the team throughout the sprint. Plot the estimated work against the actual work completed each day. This chart helps the team to see if they are on track to complete all the planned work by the end of the sprint and adjust their efforts accordingly.

It's important to note that velocity is not a measure of individual productivity but a team metric. It helps the team to understand how much work they can realistically complete in a sprint and plan accordingly. By measuring velocity consistently over multiple sprints, the team can identify trends and make improvements to their processes to become more efficient.