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Visual basic .NET question - Making an entry counter and need help? - parts of the screen (visual basic)

I am the new way of programming and I have a program that you follow the individual and the general health of the trees in a plantation of trees. Each tree has its own set of data + ID and no other tree has said identification data is then, the operation is disabled and the input is reactivated. Each record is entered in the same format so that it opens in a new window in a separate part of the program ... I wonder how a sort of counter to give each new tree would be entering an identification number so that no new structure has to create the same ID as another tree might. I want to be able to show that this identification label. If in doubt, please ask. Any advice would be very grateful. I can provide screenshots if it helps to avoid confusion.