In one sentence — Two nearby highs separated by a low form a double top; in Hurst’s model the figure can change simply because the waves reach their crests at different times.
What the reader sees
A double top looks like an M: price rises, retreats, returns to a similar level, and then moves away. A double bottom is the inverted W-shaped version. These names describe a shape; they do not yet explain why it formed.
Hurst starts with the construction used for head and shoulders: a short component oscillates while a slower component is turning. If the slower component’s high sits near the middle short crest, a head emerges. Shift the timing relationship and two crests in the sum can become nearly equal.
Hurst's phase experiment
In Chapter 3 Hurst shifts the lows of the short component slightly relative to the longer component. The result changes from head and shoulders to double top without adding a new force or a separate chart rule. The slope of the line joining the lows also depends on their alignment.
The reasoning reverses for double bottoms and inverse head and shoulders. If several components culminate at nearly the same instant, their sum can produce a sharper V turn. These are shapes in the same explanatory family, not equivalent signals with guaranteed outcomes.
What actually changes?
Phase says where an oscillation is within its turn. Two waves of equal duration can peak on different dates; waves of different duration may align only occasionally. Changing this relationship changes the height and spacing of the sum’s highs.
This idea helps move beyond naming an ideal M: scale, elapsed time, and context become part of the observation. Yet price alone does not always have a unique decomposition. Noise, trend, changing volatility, and different combinations can produce similar outlines.
Reading it without turning it into a promise
A double top is a structure to measure, not an automatic order. Before testing it, one must define how far apart the highs may be, how deep the middle low must be, when the pattern is complete, and which costs apply.
The research by Lo, Mamaysky, and Wang shows why that step matters: evaluating chart patterns requires converting them into algorithmic rules and checking them on samples. Their study does not prove Hurst’s particular cyclic explanation; it supplies a modern way to distinguish a drawing recognized after the event from a testable hypothesis.
Evidence boundary — Hurst shows that a phase change can generate a double top within his model. A similar real-world figure does not identify the components by itself, assign breakout probabilities, or prove economic value.
Sources
- J. M. Hurst, The Profit Magic of Stock Transaction Timing, Prentice-Hall, 1970, Ch. 3, pp. 56–58, Figs. III-6 and III-7 — phase shift, double top, and V turns.
- Andrew W. Lo, Harry Mamaysky, and Jiang Wang, Foundations of Technical Analysis, NBER Working Paper 7613, 2000 — algorithmic definition and empirical testing of chart patterns.
Related entries
- Head and shoulders — the same explanatory family
- Cyclic phase — the concept that changes alignment
- Chart pattern verification — the Chapter 3 framework