Thanks both.  That clears that one up for me and is affirmed by looking at the upper chart of dooglus's pair for the same time frames where we can see the 1.9% edge line showing proportionally the same jumps over the same time periods.  I was under the understanding however that the primary reason for the massive drop after Feb was more to do with the disappearance of a 'whale' rather than anything to do with usd/btc.  But maybe ThickAsThieves, your assumtion has some merit in explaining the halving in revenue between the latter pair of periods.  This is not as obvious just by looking at the charts - which lazily has been my means of keeping tabs on how my investment is doing.