DATAGRIDVIEW X,Y AXIS

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Hello i need help for my project

I have a data grid view

    | column 1 | column 2 | column 3 | column 4 |
    _____________________________________________
    |          |  Forcast |user input|user input|
    |   item 1 |__________|__________|__________|
    |          |  stocks  |user input|user input|
    |__________|__________|__________|__________|
    |          |  Forcast |user input|user input|
    |   item 2 |__________|__________|__________|
    |          |  stocks  |user input|user input|
    |__________|__________|__________|__________|
    |          |  Forcast |user input|user input|
    |   item 3 |__________|__________|__________|
    |          |  stocks  |user input|user input|
    |__________|__________|__________|__________|

in column 2 user can iput data and save it in the database and also the user can view the data. how can i determine the current cell that the data won't mix up.
the purpose of the cell to be idenfified is because of calculation like

((item 1, stocks, column 3) X (item 1, forcast, column 4))

any help. thank you.

sorry for the bad english

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