Reg.. Assigning Serial no to schedule lines using control break statements

i have sales order(vbeln), sales order item no(posnr) , schedule line .

i need the output in this below fashion using control break statement.

eg..!!

vbeln posnr schedule line

so1 line 1 1

so1 line 1 2

so1 line1 3

so1 line2 1

so1 line2 2

so2 line1 1

so2 line2 1