So I was looking at two 3x etf's and I was wondering if someone could answer a question for me about them. I was looking at (SPXL) Direxion S&P 500 Bull 3x ETF and (SPXS) Direxion S&P 500 Bear 3x ETF. From what I understand whenever SPXL goes up, SPXS is supposed to go down and vice versa. But I was looking at their daily percentage change and I found a few days when this didn't occur. For example, on 7/11/2013 SPXL closed at $47.23 and on 7/12/2013 SPXL closed at $47.21 resulting in a net daily decrease of 100*(47.21-47.23)/47.23=-0.042%. And for SPXS on 7/11/2013 it closed at $9.53 and it closed at $9.52 on 7/12/2013 resulting in a net daily decrease of 100*(9.52-9.53)/9.53=-0.10%. My question is simply how can in be that both SPXL and SPXS went down this day? Looking through the prices of these two ETFs it appears like this occurrence is really rare and that SPXS always behaves opposite to SPXL, but there are a few rare occasions when this doesn't happen. I was wondering if anyone could explain to me why this happens and also if they know of any 3x ETFs in which this sort of thing doesn't occur?
