autoinvoice run on the basis of delivery

 Hi,

If i have 1 Sales order and having 5 delivery in different dates.The grouping attribute 3 is attached to the source.

If i import the sales order,it create 5 invoices which is correct.But the problem is create 5 invoices in which sequence?

For example:

sales order=525

Delivery number

10

20

30

40

50

If i run autoinvoice for sales order 525,invoice create on what sequence basis?

I mean 

delivery 10=invoice number 1000

delivery 20=invoice number 1001

delivery 30=invoice number 1002

delivery 40=invoice number 1003

delivery 50=invoice number 1004