Thanks for your response and the sample form which I understand.
Editing the embedded datasource file I add my own xml data which worked fine.
As my forms are browser my ideas to add my own store number and names to the xml would not work.
Instead of using the xml I tried with a sharepoint list with 2 columns.
On selecting a store number it will always
pick the first store name in the sharepoint list and when selecting another store number it will still remain on that first store name.
Any ideas, a rework of the formula I guess
M