Okay, I think I am being particularly dense here.
I have been building databases in FM for a few years now, okay, there's been a bit of trial and error... I learn by playing.
SO, after changes in the workplace something that I built a while ago wasn't quite suitable. I have started over from scratch.
Employees table I have put a pk_EmployeeID, fk_CompanyID and a OustationID
Companies with a pk_CompanyID - auniqueID... ( I have used the new get(UUID) function) There's also a fk_OustationID
Outstations with a pk_OustationID ( as above) and also a fk_company ID and a fk_employeeID too
We have Companies, each company could potentially have a few locations (Outstations) One company may have many Outstations - (One to many
Some companies don't have an outstation, so that an option.
We have employees, an Employee table with records would normally be set up to be assigned to Company and if applicable their outstation that they're are assigned to. It's unlikely but over time their company or company or outstation could possibly change.
I do have layouts that are in the context of Employees table have merge fields, I use these to produce documents such as contracts of employment.
I seem to be able to get the employee's company to change and display a merge field, but not the outstation, ( either display, or change)
Any help would be, as ever, gratefully received.