I worked in a company who measured productivity by attributing a score based on the Fibonacci scale. But they were doing this when the feature was done.

By doing that, it was fairly easy to give a relevant score to each feature.

Engineering team was doing this to measure solely engineering productivity, but product team could do this as well to measure added value to the company.

By tracking the start/end date as well for each feature, you can then measure productivity at any time scale you want.