Productivity is measured based on output per labor hour. In drywall terms, it is the square footage amount one board hanger can hang in one hour. To measure productivity, one must know what the output per hour is, and in the case of drywall hanging most contractors look at it historically rather than currently.
In other words, contractors look at their job costs and see negative variances in the amount budgeted week after week, and month after month until the job is done. Once the job is done, they can say they did really well on the framing, OK on the taping, but the drywall hanging didn’t go so well.