It sounds like your relationships are failing to match to a record in a related table for these two products and thus a value that should be referenced in that related table is replaced by a null value and you then get 0 as the computed result.
That's just a guess. To suggest more or how to fix such an issue would require a more detailed description of your tables, relationships and the calculations that use them to get the correct result.
Thanks for this but I'm not sure. I am just taking a cost force of 11 (variable depending on the product) then multiplying it fixed number (taken from a Value list) and dividing it by the currency exchange rate again a number taken from a Value list. As I said it works on all but 2 records. The initial data came from a Numbers spreadsheet which I dropped onto Filemaker. I have deleted and re entered the records without any change. When I try and enter new records the calculation is O. I've checked all elements are numbed etc. The products are entered by a form and everything has gone in the same but these two records give me a zero result.
Which still sounds like a case where two products records are failing to look up a value from a related table.
To suggest more or how to fix such an issue would require a more detailed description of your tables, relationships and the calculations that use them to get the correct result.
How would it be best to describe the tables & relationships? Can I send a copy of the database over?
Try using the "upload an image controls" to upload a screen shot of the relevant portion of Manage | Database | Relationships. Please include additional text that helps others to identify which "box" is which in that image. Also be careful to only upload files of one of the file types specified. If you upload a PDF it appears to upload, you don't get an error message, but no image appears in your post.
You can also copy and paste the calculations from the specify calculation dialog directly into Post a new Answer to share the exact syntax of your calculation expression.
Think I've cracked it. I was using too many value lists when I didn't need too. Knocked them out, simplified the tables as they didn't need Value lists and the 0 is now a real number.
Thanks for replying to my post. Your response made me think and helped be find the solution.