Field help (FORQTY) 

You can only use this field if you have used a predefined 'Component selection' formula in the field Selection formula (field FORSEL). Instead of entering a quantity per component option/variant you can use a predefined 'Component quantity' formula to calculate the quantity for each component that is needed to make the parent product.

 You can change the component quantities calculated by the formula when this BOM is added to a sales transaction.