1820.66 is the October 2014 low
The S&P is down 2.47% and currently trades at 1835. The low extended to 1825.00 – close to the Ebola driven low of 1820.66 back in October 2014. From the high, the index is down about 14.3%.  The 38.2% of the move higher from the 2011 low comes in at 1729.82. A 50% correction of the move higher would go all the way to 1604.74. That is a 50% of the move higher. A 50% decline like what was seen in 2000 and 2008 is something different.  A 50% decline in the S&P from the high would be to 1065ish. That would be quite a drop from  here.