To preface, I'm taking a macroeconomics class and we're learning about measuring GDP. The textbook says that there are two main ways to measure GDP: the expenditures method and the income method.
The expenditures method can be represented like so:
$GDP = C + I_g + G + X_n$
where $C$ is personal consumption expenditures, $I_g$ is gross private domestic investment, $G$ is government purchases, and $X_n$ is net exports.
The income method is more complicated, and looks like this:
$GDP = I_n - I_f - C_c + s$
Where $I_n$ is the national income, $I_f$ is the net foreign income, $C_c$ is the consumption of fixed capital, and $s$ is the statistical discrepancy.
$s$ is calculated by subtracting the expenditures method from the income method, in order to make them the same.
What is the point of having the income method if it relies on the expenditures method? I get that it would be useful for statistics, but why use both?