Open Quotationer–> Select Configuration–>Select Product Information–>Click on add item with specification–> Enter Product Details and equations–> Add.
example: Consider your item is marble, Then you can give the formula to calculate its quantity as ‘item specification’ ie, (length*Breadth)
A specification window will open when you are selecting this item to a quotation where we have to enter breadth and length of the item. then the quantity of the item will calculate automatically.