I have the cuttingwork with bedsheet =12 and duvett=9
I WANT in the sewdetail form ,after filling the duvett and bedsheet there come a warning preventing duvett to add or adding bedsheet is okay also a report showing that quantity of the product can be added or not
(this product field is from cutting workdetail table)

I hope that you can help me...thanks alot

Liem Richard's work always works, and if it doesn't, he will add it in an addendum to let you know.
If you want to prevent duplicates in your detail table, just make the product ID indexed with no duplicates. That will fix the problem.

A multi-field index can prevent this.  Richard has several videos about indexing.

Indexing
https://599cd.com/blog/display-article.asp?ID=2361

Preventing Duplicates
https://599cd.com/blog/display-article.asp?ID=2187

I am sorry....
I did not mean RICHARDS vba was wrong.

I used RICHARDS VBA in combobox of my form , so I need another way .

Is it right that theree is a different way to prevent duplicating in a combo box value on a form.

I hope you can help me
Thank you very much

Populate your combo box with a Query, use the SUM option to limit the list to one item. ie; Joe Smith, David Smith, Samantha Smith.   Sum by last name, will give you only one Smith.