#20 ATR Calculated Incorrectly
There are two bugs in AverageTrueRange.java regarding the calculation of average true range.
First error: line 217 and 218 should use absolute value:
highPrevClose[i] = high - prevClose;
lowPrevClose[i] = low - prevClose;
Not using the absolute value gives the wrong result, and makes the lowPrevClose calculation worthless (it will never be used, because without taking the absolute value, highPrevClose is guaranteed to be greater).
Second error: Chartsy uses a simple moving average for ATR. It should use Wilder's smoothing method. Wilder's smoothing method is equivalent to EMA(period*2-1).
The complete description of ATR appears on pages 21 and 22 of "New Concepts in Technical Trading Systems" by Wilder.
Chartsy seems to be the best open source charting program (by far). I really hope you guys get this fixed soon.
