There are times when there is an exponential increase in volume in the last minutes of a trade session. On a regular basis the closing price would mean that it was the last traded price for the day but that doesn’t always hold true. Sometimes due to heavy volume all the orders and their resultant price changes aren’t updated in real time, the actual closing price determination takes some time to process due to the heavy volume and is sent over after the session. By that time the charting software has stopped taking quotes and hence the price isn’t updated with the official closing price for the session. There is also the factor of the consolidated quote system which again has the same affect as the aforementioned. And this happens with opening prices too at times. Best practice would be to check the NSE website for the official opening and closing prices.