1576.1 was the 2007 peak high.
From 2137.1 (the 2015 all-time high) a . of the rise from 672.9 ( 2009 low) to 2137.1 would be 1577.8.
.618 of the price distance from 1576.1 (2007 high) to 672.9 ( 2009 low) was 558.1776 points, which, subtracted from 2137.1 (2015 high), would yield 1578.9224
Assuming an count wherein 2137.1 was the start of the market, and 1833.5 was the bottom of a 1st wave down, and the correction to 1995.4 was the top of a 2nd wave up, then from that point a subsequent 1.382 downward extension of the 1st wave would reach 1575.8 in a 3rd wave. 1.618 would be a more typical 3rd wave extension, but given the existence of the prior market peak at 1576.1 it seems a reasonable enough level to expect hard resistance which might end the 3rd wave.
Here we have a combination of significant wave proportions, both historical and hypothetical, and significant price points, which, when applied as above, all point to the same price level within a margin of only 3.1224 points. So, I suspect that 1576-1579 could be taken as one important downside target in the initial stages of this correction.