Immediate definition
In plain words — “Trading by logic” means deciding through a written sequence: market first, then security, signal, risk, and execution. It does not mean that the sequence can know the future.
Chapter 8 of The Profit Magic of Stock Transaction Timing brings together the tools Hurst introduced earlier. It offers no new universal indicator. Instead, it shows how envelopes, moving averages, trend lines, scanning, and tracking are meant to contribute to one decision. Its clearest teaching value is the explicit chain, because each stage can be inspected separately.
The operating chain
The first stage is the cyclic market state. In the 1 November 1968 case, Hurst reads three Dow components and decides that a short bullish window remains. Selection follows: the scan brings Screw and Bolt into the shortlist. Analysis turns that candidate into a conditional thesis, using periods, a nest of lows, valid trend lines, and a price zone. Execution then includes order, fill, trailing level, and exit.
This breakdown prevents a common mistake. An analysis may be internally coherent and still lose money. “Logical” describes the connection between premises and actions; it does not certify the premises, the data, or future effectiveness.
What remains useful today
The strongest principle is to prepare observations before they occur. Universe, regime, security, entry condition, invalidation, and exit should be recorded before the outcome. The same applies to the rule version: if a parameter changes after the next chart is seen, that outcome no longer belongs to the original test.
Modern technology changes the execution layer. An alert, quote, order, and fill carry different timestamps; spread and liquidity may make the theoretical price unrealistic. A current reconstruction must therefore preserve unexecuted signals, rejected orders, costs, slippage, and open positions. The finished chart alone is insufficient.
From case report to evidence
The chapter presents a model trade and a six-week experiment. They are useful historical sources for understanding how Hurst applied his method, but they are not independent validation. The book is both protocol description and results report; Cyclepedia does not hold the complete primary memorandum file mentioned by Hurst and cannot verify every rejected candidate.
A modern evaluation would separate development and validation, use the data available at each date, freeze the rules, and retain an untouched period. It would also disclose how many variants were tried: searching across many signals raises the chance of finding a convincing configuration by chance.
How to read this entry
The source-checked label means that the reconstruction was checked against
Chapter 8. It does not mean that Cyclepedia replicated the performance or that
the method suits a particular market, instrument, or reader. The chapter's
most durable contribution is an auditable process: a decision should be
reconstructable without inventing explanations afterwards.
Sources
- J. M. Hurst, The Profit Magic of Stock Transaction Timing, Prentice-Hall, 1970, Chapter 8, pp. 123–140 — primary source for the historical sequence.
- Campbell R. Harvey, Yan Liu, and Heqing Zhu, … and the Cross-Section of Expected Returns, NBER Working Paper 20592, 2014 — multiple testing and evidentiary thresholds; it is not a test of Hurst's method.
Links
- Cyclic market state — context for the case.
- Screw and Bolt case — the operating sequence.
- 1968 trading experiment — results and limits.
- Selection and tracking — from market universe to shortlist.