The market isn't up until we break through this line

The market might have been "up" for most of Tuesday's trading, but it never broke through this key trendline—the one thing that actually matters.

This is a chart of the S&P 500 going back five full trading days, along with a green trendline showing the prevailing direction. Every time the market touched the line, it fell right back down.

This is why just looking at a single day's performance doesn't actually tell us if we have broken back up. Yes, we were up a lot for most of Tuesday, but that was starting at such a low base. Comparing a price to an arbitrary 4 p.m. cutoff doesn't tell you the full story of the overall minute-by-minute market moves.

That downward trendline still rules the markets until it's been broken. We could be up again Wednesday, even another 50 points on the S&P, over 2.5 percent, and still have not broken back above the trendline. It might touch the line and fall right back down.

This will be something to watch in the coming days. The SPX will need to be at least above 1,925 for us to safely say we have made it through this short-term mess.