National income is a measure of the total value of goods and services produced by a country over a specific period of time, usually one year. It is used to assess the economic performance and standard of living of a nation. There are several measurements of national income, including:

1. Gross Domestic Product (GDP): GDP is the most commonly used measure of national income. It represents the total value of all final goods and services produced within a country's borders in a given year. GDP can be calculated using either the expenditure approach (summing up consumption, investment, government spending, and net exports) or the income approach (summing up wages, profits, rents, and other forms of income). GDP can be measured at current prices or adjusted for inflation to provide real GDP.

2. Gross National Product (GNP): GNP measures the total value of all final goods and services produced by a country's residents (both domestically and abroad) in a given year. It includes the income earned by citizens and businesses from their investments and activities outside the country. GNP is calculated by adding net income from abroad (the difference between income earned by domestic residents abroad and income earned by foreign residents within the country) to GDP.

3. Net National Product (NNP): NNP is obtained by subtracting depreciation (the wear and tear of capital assets) from GNP. It provides a measure of the net value of the country's output after accounting for the capital consumed in the production process.

4. National Disposable Income (NDI): NDI is the amount of income available for consumption and saving by the residents of a country after deducting taxes and adding government transfers. It represents the actual income that individuals and households have at their disposal.

5. Per Capita Income: Per capita income is obtained by dividing the total national income by the population of a country. It provides an average measure of income per person and is often used to compare the standard of living across countries.

These measurements of national income provide valuable insights into the economic performance, growth, and distribution of wealth within a country. They are used by policymakers, economists, and researchers to analyze and make decisions regarding economic policies, investments, and development strategies.