Calculates the Average True Range indicator and returns its value.
[in] Symbol name on the data of which the indicator will be calculated. NULL means the current symbol.
[in] Timeframe. It can be any of ENUM_TIMEFRAMES enumeration values. 0 means the current chart timeframe.
[in] Averaging period.
[in] Index of the value taken from the indicator buffer (shift relative to the current bar the given amount of periods ago).
Numerical value of the Average True Range indicator.