can you please explain the point: adjustment of national income in use of index nos in eco in detail it is not clear

Index numbers are used to adjust national income on the basis of constant prices. This is done to determine the real change in national income as compared to the base year. For example, the national income of India in 1980 was 1000 crore and it increased to 3000 crore in 2015. Now this increase is  a result of increase in real national income as well as an increase in price level or inflation. Index numbers adjust this national income for inflation and determine the real increase in national income.

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