Stock market indices are useful tools for understanding market trends and performance. The BSE SENSEX tracks 30 major companies on the Bombay Stock Exchange, with its base value set at 100 in 1978-1979. It is calculated using each company's free float market capitalization. Similarly, the NIFTY index tracks 50 major National Stock Exchange companies, with its base year being 1995 and base value at 1000. Both indices are weighted averages and act as benchmarks for measuring portfolio and economic performance in India.