I'm thinking that summarizing of field A's content should be within the script, but don't know which script functions to use. Other than that the content of field B should empty when ever leaving these found records.
You said the magic word!
Look through the help index on FMP and learn about summary fields. They would NOT be within the script, a summary field is a specific type of field made to do exactly what you are trying to accomplish. Another tool for your future FMP toolbox!
I've tried to follow the instructions in the help menu, but the field won't display any value. Can you tell what the options would be, when I want to sum the numbervalue of a specific field across all found records?
-Field with the value wishing to be summed
But that does not display any value in the new field..
That should work for you. Describe the layout where you've placed this summary field where it isn't displaying any value. Is it in the body, sub-summary part, or...?