Populate data from 1 field to another in the same Module.

Populate data from 1 field to another in the same Module.

I've read several of the post on doing this but can't seem to get mine to work. This is the in the same Module called BREAKDOWNS. I am attempting to populate the date is one field with data from another. The fields are in the same module, however, one of them is a lookup field to another module. Here's what I have.

Field1: Production Title (Lookup field to Module PROJECTS)
Field2: Production Title Catch (Single Field)
Field3: Production Title Calc (Formula Field to do the calculations)

I'd like to add the data from Production Title field to Production Title Catch Field after user updates Production Title field.