Hi , I have one main form and 2 child forms, there is no link between all these forms, every child form is bounded to a query, lets give the name of child forms, Child1 have the inventory information, and child2 have the ordered information,
now what i'm doing , in child2 i have sum of the products deliverd to customer, in this form i have 3 fields,

Product_Code SumofQuantity CostPrice
A 12 have to know?

now i want to show the cost price , but i need to take this cost price form the child1 form where i have the inventories, in child1 form i have 5 fields,

Inventory_Code Date Product_Code Quantity Price
001 20-aug-02 A 5 20.40
002 22-aug-02 A 36 18.10

now i need to take the product_code and SumofQuantity from Child2 and have to write off from the Child1 form and then need to show the cost price in child2 form, i need to use event procedure in the Cost price field which is in the Child2 form , but how i will know that which product i have sold first, i need to use FIFO method, first i need to sale the first inventory if it finish then got to the 2nd inventory but how shuld i contorl this check?

here is the example for better understandidg,

code date product quantity cost_per_unit Total value
001 20-aug-02 A 5 20.40 102.00
002 22-aug-02 A 36 18.10 651.60
Total 41 18.38 753.60
The cost per unit is calculated as Total value/Total quantity , now i sale 12 of these units, leaving 29 in stock
the value of the sale is calculated as follows Using FIFO method (First In First Out)
5 units at 20.40 = 102.00 (these are from the first inventory leaving none left over)

7 units at 18.10 = 126.70 (these are from the new inventory leaving 29 left over,


12 units combined valued 228.70 (19.06 each)

the 29 units remaining in stock all come from the new inventory and have a valued of 524.90 in total (18.14 each)

please give me any advise how i can solve this task , i realy need to solve it, since last 2 week i'm trying to solve it but no success, may be some one can help me.
Thanks in advance