The National Stock Exchange (NSE) has changed the methodology for calculating the Price to Book (PB) ratio of the Nifty index, leading to a decrease in its valuation measure. The PB ratio dropped by nearly 20% without the index falling, making Nifty's valuations cheaper. The change involves factoring in the net worth of each index constituent at the consolidated level in the annual financials, as opposed to standalone earnings. The PB ratio compares market price per share to book value per share and helps investors determine whether a stock is overvalued or undervalued.