Modules & VBA :: Automate Line Numbers And PO Numbers

I have 2 fields that I would like to automate if possible

One field is called "p/o number" and another field called "line no"

These fields are part of an ordering database

Let say I have 200 items to purchase form 10 suppliers

And form example 20 items from each supplier

What I do at present is put the order number on each line item and the line number

example

p/o number line no

1 1
1 2
1 3

2 1
2 2
2 3
2 4

What I want to do is just put the first po number in the required line . Put the first line number in i.e. "1" and the macro will complete all the p/o numbers and line numbers for me as per the ones marked in red.

Example

1 1
2 2
3 3

2 1
2 2
2 3