What is the formula used by zerodha to calculate ATR

I am trying to build a Renko chart and analyze my strategies. But the ATR that is getting calculated by me is different from what zerodha is displaying. I am using the following link for ATR calculation. -> https://stockcharts.com/school/doku.php?id=chart_school:technical_indicators:average_true_range_atr

I am calculating for 1min intervals. And the ATR period is tentative, but i am maintaining the same periods in both my calculation and the ZERODHA charts.