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By evankoh posted on 1 Jun 2017  -  27,392 views


If you looked at your portfolio report these past few days, you might have noticed an unreasonable increase (typically well beyond 1000%) in your portfolio time-weighted returns, as well as a sharp increase in ES3's monthly volatility (>20%).

Firstly, I am very thankful to users who took the time and effort to report this issue. Some users even went a step further to take screenshots to ensure that I can easily understand the problem. In fact, several users did so independently. It is very important for users to report irregularities because many a time, I do not even see these errors as everyone uses StocksCafe differently.

Next, I would like to explain why it happened and why it is unlikely that it will be error-free going forward.

For this particular issue, there are actually two reasons:
1) Generating portfolio report is a computationally-expensive task. As the number of users for StocksCafe continue to increase rapidly, I have been tuning it to run as fast as possible, and in the process introduced the bug of wrongly computing portfolio time-weighted returns.
2) With the expansion to Hong Kong and Malaysia markets, there are days when ES3 did not trade, but I still computed the daily return of it, which lead to the sharp jump in volatility (this likely happen to users with stocks outside SGX).

These issues affected about 1% of the users.

In general, the reason why it is unlikely to be error-free going forward is simply because StocksCafe is continuously expanding to new markets and having new features added to it. With limited time resources, it is a tradeoff between the speed of releasing new features vs probability of errors with the new release. Of course, I will perform checks before releasing new updates, but there is still a chance of errors slipping through the cracks.

What I would typically do after discovering an issue (and fixing it) is to write a checking script to at least quickly realize it if the same issue were to happen again in future.

Therefore, please continue to report to me whenever you see irregularities, and let's improve StocksCafe together! Thank you!

Happy investing!


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