Why has the value of historical candles on my chart changed after a refresh or opening a new chart?
When you open a chart, live candles are formed on your computer or mobile using the ticks or prices streamed from Zerodha’s end. Historical candles or the candles already plotted when you open a chart, are stored at Zerodha’s end using the market data that is received from exchanges.
Once a chart is opened, the data used to form the candles on the chart could be a subset of the actual data Zerodha receives. You may receive lesser ticks based on the speed and uptime of your internet. This means that the candles that get plotted on your device could be slightly different from the candles that get saved at Zerodha’s end for historical data. When you refresh your chart or open a new chart, Zerodha stream the historical candles calculated which replaces the candles that were plotted from the time you opened the chart. This is the reason why a chart can look slightly different when you refresh or open the same chart that you were viewing.
Adjusting the opening price of the day
The opening price of the day for the charts plotted using the market data may not be exact market opening due to exponentially higher ticks at the market open even at our end. So Zerodha adjusts the opening price of the day at around 9:20 AM using the actual open price that gets published by the exchanges.
In the case of stocks, this open price is the pre-market opening price of 9:07 AM and for F&O it is the actual opening price that you see in the market depth. So once this opening price is adjusted at Zerodha’s end by 9:20 AM and if you refresh the chart or open a new chart, the historical candles will show the actual opening price of the day published by exchanges and not the opening price that was captured by the candle at your end.