match numbers based on conditions and show the difference

[coolmob]

i am making a personal stock keeping workbook. i get packages of different materials containing items of different weights. like i get a box of copper tubes containing 10 tubes each having different weight. like wise for iron and other materials.

now i have made a sheet where i feed the name of item using vlookup and the enter the details of tubes in each package. a similar sheet for tubes sold. i am looking for a formula which would reference the inward sheet, sort all data for one particular product like copper, take all the different weights and then subtract the ones in the outward sheet and display each individual weight in the stock in hand in a separate sheet.

each product will be entered on daily basis so a certain product will have multiple entries in both inward and outward sheet in no particular sequence with different dates and different weights. the formula should be able to generate the stock in hand on the fly for each product by comparing both inwards and outwards as and when data is entered in inward or outward sheet.

thanks