I’m looking at Reading 17 Exhibit 1 diagram about the simple economy and its circular flow.
I can see 4 elements - inputs, outputs, income and expenses.
In section 2.1 GDP, it proceeds to say that GDP can be calculated only in two ways - based on outputs and inputs.
Why are expenses and income not used to calculate GDP as well? All of these would equal obviously, but why is there only two ways to calculate GDP?