What is the underlying formula used to calculate the default range in Renko charts for a script, given that it doesn't align with the conventional ATR14 method?
The default brick size in Renko charts is calculated using the Caveman algorithm . This algorithm uses 300 aggregated bars of data on the chart (i.e. about a year for daily charts and about 5 hours on a minute chart) and comes up with a reasonable default value. So, the default range will vary depending on the asset (instrument/scrip) viewed.