If every tube is a record, the coil serial number (or perhaps better, the pk from the coil table) would have to be part of that record. If not, then the coil sn would be part of the batch record. A split form is not the right form for this because it is only a form with 2 views of the same data. You should have a form/subform design - perhaps form and 2 subforms. Can't say without knowing the relationships involved between inputs and outputs.
The integrated steel company I worked for has a couple of tube mills but I didn't have much to do with them.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.