About master purchase orders
To control the ordering and arrival of materials at a job site, use a master purchase order. Think of the master purchase order as a contract with the vendor, which lists all the materials you intend to purchase over the course of the project. You might even supply each of your vendors with copies of the master orders.
From the master, you create smaller purchase orders for the materials necessary to complete the next series of tasks. The master tracks the total quantity of items ordered and canceled for a particular vendor and job. After creating the master purchase order, you can create all the smaller purchase orders to ensure you have accounted for all materials on the master purchase order. You then only need to assign the appropriate delivery dates and print the purchase orders as you need them.