# Yahoo Finance (CSI) Data Quirks. Or Why is the ROC not Stable?

Rotational strategies on ETFs have been a common occurrence on this blog, and I have been using something similar for real life trading for about two years now. Readers of this blog may have also noticed concerns about the stability of the computations of such strategies. At the end it turned out be a quirk in the data feed, not accounted for in my code.

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