Thanks SURESH
I'm looking for another way to perform it ie :
for production order of 8000 kg, i must confirm at the 1st operation 8200 kg, then at the 2nd 8100 kg, and at the 3th and last 8000 kg. So as i have in the last operation the planned quantity of the production order.
But it's also possible to meet the business requirement with scrap parameters.