CHART COLLEGE · THE CLASS

The big gap down on heavy volume

What the market says

"A 10% gap down on heavy volume is either a bounce waiting to happen or the start of a slide."

The pattern, as the memory screens it: s.gap_pct <= -10 AND s.rvol >= 3, liquid names ($50M traded on the anchor day, above $5), 2019 to the latest close. A name that is normally thin can qualify on a spike day, so the instances lean toward the names that spike. Questions this lesson answers:

Bounce or slide: what did the next week actually look like?
Did the ones already far off their high behave differently?

What the charts did

The next session was no different from an ordinary day: 50% of 4,505 closed below the anchor, against 49% of ordinary days. Median next-session move +0.0%.

A week on, 46% were above the anchor, fewer than the 55% of ordinary days; median -0.7%, and the middle 80% ran from -12.9% to +12.5% (ordinary: -6.1% to +6.8%).

A month on, 47% were above the anchor, fewer than the 53% of ordinary days; median -1.0%, and the middle 80% ran from -22.9% to +21.9% (ordinary: -12.6% to +13.5%).

Three months on, 49% were above the anchor, fewer than the 54% of ordinary days; median -0.8%, and the middle 80% ran from -36.2% to +44.6% (ordinary: -19.9% to +24.8%).

A year on, 47% were above the anchor, fewer than the 56% of ordinary days; median -4.6%, and the middle 80% ran from -67.8% to +92.6% (ordinary: -38.2% to +58.2%).

The week after this pattern is 2.0 times as wide as an ordinary week. That spread, not the median, is what the pattern tells you.

4,511 instances across 2,110 stocks, 2019-01-02 to 2026-09-18. The ordinary-day base rate is every liquid stock-day on one Wednesday a month over the same years.

Raw move from the anchor close	Instances	Share above	Median	Middle 80%	Ordinary day: share above	Ordinary day: middle 80%
Next session	4,505	50%	+0.0%	-7.0% to +7.5%	51%	-3.0% to +2.9%
1 week (5 sessions)	4,491	46%	-0.7%	-12.9% to +12.5%	55%	-6.1% to +6.8%
1 month (21 sessions)	4,449	47%	-1.0%	-22.9% to +21.9%	53%	-12.6% to +13.5%
3 months (63)	4,293	49%	-0.8%	-36.2% to +44.6%	54%	-19.9% to +24.8%
6 months (126)	4,085	47%	-2.5%	-49.7% to +60.5%	55%	-27.6% to +35.7%
1 year (252)	3,602	47%	-4.6%	-67.8% to +92.6%	56%	-38.2% to +58.2%

How it looks

Two dozen instances chosen at random, each cut at its own anchor: dark is the run-in, orange is what followed. Pick how far ahead to look; the tiles regroup by what happened.

Try it on any chart

Pick any ticker and date on the wall and the memory shows you the charts that looked like it. The class is the pattern in bulk; the wall is one chart at a time.

JSON · All lessons · built 2026-09-21