Not sure that your two table set up really makes since, but....
If you go to Manage | Database | Relationships, you can drag from the serial number field on one table to the serial number field in the other to link the two tables by serial number.
Then, on your layout based on Table A, you can include fields from Table B. If there is no matching record in Table B, these added fields will show as empty.
I have done the relationship like the image below.
I have dragged a find into layout A using the field tool and then pick just for testing model from table B, but the field stays empty even if i pick a serial number that is in both tables.
Obviously i am doing something wrong
If the field stays empty after you enter a serial number and click a blank area of the layout, then the values of the two fields do not match. Make sure that both fields are the same and correct data type. Make sure that exactly the same data is entered into both. If these are text fields, a single trailing or leading space can keep them from matching.
Still missing something. Fields are exactly the same. Both are text. Both says "indexed" under options/comments
Then I will repeat that either the values are not truly equal or you haven't defined the relationship as you think you have. This is basic "Relational database 101" stuff that appears in every relational database so if it didn't work, systems like FileMaker wouldn't exist.
If you want to pursue this further, perhaps you can upload a screen shot of the relevant portion of "Manage | Database | Relationships"?
Thanks for the help. Hopefully this is what you require?
Sorry. I had forgotten that you'd previously uploaded the one screen shot.
What I can't see are the values of Serial # in customer detail nor the supposedly matching values in "loaded Proact Ma..."
All you need is for one character to be different even an added space character at the beginning or end of the serial number in the record in one table and not in the other and your records will not match.
You might try this test:
On the layout shown, copy the entire contents of serial# to your clipboard.
Switch to a layout based on the other table.
Enter find mode
enter == into the serial number field from this table
paste your copied serial number into this same field to the right of the second = operator
Does it find a record?
If it does, what do you see in the Model field?