calculation of unrealised profit by using net method on TNCA

I want to ask a tutor that realizing the PROFIT means that when the group sold the item to the third party it becomes realised PROFIT but in your net method you are realizing the profit on the basis of useful life life of an ASSET . Life of an TNCA can not be used to realised profit because it is a life of asset not profit life so what type of method is this please explain what are you trying to do with this