Tracking # of inches of welding?

We use Vantage to track quantities of items to complete but there have been questions as to whether we can additionally track inches of weld.

For example, we have an operation to weld 3 beams and the operation has a total duration of 40 hours. What if we wanted the welders to record the number of inches welded each day, alongside the quantities of beams completed?

We thought of adding two additional fields at the JobOper level, one for units and the other for U/M (example: 6000 & inches). At the MES screen I'd have to add some fields: boxes to show the number units & U/M remaining for the Operation and another to allow data entry of inches completed on that day.

Adding the fields is the easy part. Making the math work is harder (remaining units based on what has been recorded).

What are thoughts on the best way to do this?