02 April 2009
For the premier Bombay Stock Exchange that pioneered the stock broking activity in India, 128 years of experience seems to be a proud milestone. A lot has changed since 1875 when 318 persons became members of what today is called The Stock Exchange, Mumbai by paying a princely amount of Re 1.
Since then, the country's capital markets have passed through both good and bad periods. The journey in the 20th century has not been an easy one. Till the decade of eighties, there was no scale to measure the ups and downs in the Indian stock market. The Stock Exchange, Mumbai in 1986 came out with a stock index that subsequently became the barometer of the Indian stock market.
Sensex is not only scientifically designed but also based on globally accepted construction and review methodology. First compiled in 1986, Sensex is a basket of 30 constituent stocks representing a sample of large, liquid and representative companies.
The base year of Sensex is 1978-79 and the base value is 100. The index is widely reported in both domestic and international markets through print as well as electronic media.
The Index was initially calculated based on the "Full Market Capitalization" methodology but was shifted to the free-float methodology with effect from September 1, 2003. The "Free-float Market Capitalization" methodology of index construction is regarded as an industry best practice globally. All major index providers like MSCI, FTSE, STOXX, S&P and Dow Jones use the Free-float methodology.
Sensex is calculated using the "Free-float Market Capitalization" methodology. As per this methodology, the level of index at any point of time reflects the Free-float market value of 30 component stocks relative to a base period. The market capitalization of a company is determined by multiplying the price of its stock by the number of shares issued by the company. This market capitalization is further multiplied by the free-float factor to determine the free-float market capitalization.
The base period of Sensex is 1978-79 and the base value is 100 index points. This is often indicated by the notation 1978-79=100. The calculation of Sensex involves dividing the Free-float market capitalization of 30 companies in the Index by a number called the Index Divisor.
The Divisor is the only link to the original base period value of the Sensex. It keeps the Index comparable over time and is the adjustment point for all Index adjustments arising out of corporate actions, replacement of scrips etc. During market hours, prices of the index scrips, at which latest trades are executed, are used by the trading system to calculate Sensex every 15 seconds and disseminated in real time.