I was implementing an RSI indicator when I found that there are two different versions frequently attributed to J. Welles Wilder. The version described on Stochcharts.com seems to be the original Wilder version. By comparing the output from my implementation of this indicator I found that this is the version used by MetaStock. However, QuoteTracker seems to use a different version as its chart did not match my implantation or that in MetaStock. Searching around a bit more I found another definition of RSI on Wikipedia which is calculated using EMAs. I implemented this version and found it appeared to match QT for the first n periods but after that the results started to differ. Iâve compared my EMA class against QuoteTracker and found that it uses the same method to set the initial value, so the EMA is not the cause of the discrepancy and I canât see any other issues. Iâm therefore wondering if QT has not only implemented a variation of RSI that isnât the true Wilder version but has also implemented it wrongly. Iâd be very grateful if someone could confirm whether itâs me or QT thatâs getting it wrong. Hereâs my output for a 5 period RSI using the EMA version defined on Wikipedia: Hereâs a 5 period RSI in QuoteTracker for the same data: As you can see QT seems to match my output for the first 5 periods but the results differ after that. It dips to nearly 50 at 09:35 while my results say 72.6. Itâs also dead on 70 at 09:36 and 09:37 while my results say 78.1. So is QuoteTracker getting its RSI calculation wrong or is it me? Is it maybe using a third method that I havenât seen? Thanks for any advice you can offer on this issue.