Delivery performance is based on several factors.
- If you produce enough to meet demand, then your delivery index will be high, as your customers generally can buy your goods as soon as they want them.
- If you don’t produce enough to meet demand, then your delivery index will decrease as your customers have to wait for goods to be delivered to your retailers. ie. your retailers will stock out of your products several times per year.
Your delivery index will also be affected by how much excess demand you have. In general, if there is only a little bit of excess demand then your delivery index will remain relatively high, and it will decrease by more as the excess demand increases.
If you can manufacture goods quickly and keep a reasonable number of weeks of finished goods on hand, then in general your delivery index won’t be affected too badly.
You can read more information about this in the Player’s Manual, Chapter 3: Operations.