I have created a subform which is to allow the entry/display of order lines on a purchase order form.

However, I would like each line to have a line number. The line number would defualt to 1 when a new purchase order is created, and would increment by 1 when each order line is added on the subform. Obviously, should the purchase order already exist, then the line number needs to be equal to the last line on the subform + 1

Im very new to access, I initially thought autonumber would do this, but it doesnt reset when I create a new purchase order.

Any help, ideas, code would be appreciated greatly.