How to get UniDBGrid.columns.editor text for calculated field

[david_navigator]

I have a dbgrid linked to Table A.
I have a calculated field in my database, depending on the value of field 1, the data displayed in calculated field 2 either comes from table X or table Y. 
This works well.

I also have a UnitEdit control as the Editor control for field 2.

 

If the user creates a new record in the grid, then I want to get what they typed in column2 (UniEdit) and save it in either table X or table Y as appropriate.

 

However I don't seem to be able to get this data.

I presume that because field 2 is calculated, none of the field events (onChange, OnSetText) get fired nor is the field actually updated i.e in the Table A onBeforePost event, field 2 has the value that was calculated rather than the value the user typed in to the control.
How can I retrieve the text in the control ?

I've tried UnitEdit1.text, but that always seems to return the design time value of the UnitEdit1.text property, rather than what the user typed.