Dear Nhi Phan,
Suppose that a purchase order for 200 pieces of a product that should have been received three days earlier has not been received yet. Because of this, a sales order line for 75 pieces of the same product that should have been shipped yesterday has not been shipped.
A customer calls and wants to order 150 pieces of the same product. When you verify the availability of the product, you find that there is another purchase order for 100 pieces of the product that will be delivered 10 days later a sales order line for the product and enters 150 for the quantity. Delivery date control is ATP. Therefore, the ATP data is calculated to find the earliest possible ship date. Based on the settings, the delayed purchase order and sales order are considered. This results in the ATP quantity for today is 0. Tomorrow, when the delayed purchase order is expected to be received, the ATP quantity is calculated to be larger than 0, in this case it is calculated to be 125. However, 10 days from now, the ATP quantity becomes larger than 150 when the additional purchase order for 100 pieces is expected to be received. The ship date is set to 10 days from now based on the ATP calculation.
So you can tell the customer that the requested quantity can be delivered 10 days from now.
Hope its clear now.