Okay, in that case you will need to use a Custom Form.
The problem with native forms is that the input values are only written to the underlying table when the form is submitted, so you cannot access them to perform any calculations prior to that. With a custom form, the input values are written to user specific columns as they are entered, and so you can “do stuff” with them.
The general approach:
- Create a details screen, and add whatever input components are required
- Target each of the input components at a user specific column
- Use those columns to do your calculations, and display the results
- When the form is submitted (you’ll need to add your own submit button), take the values in the user specific columns and use them to create a new row using an Add Row action.