Who this entry is for — Readers who want to construct and interpret an FLD without reducing it to the imprecise formula “price shifted half a period”.
Source boundary — “Cyclic Analysis” (1974) cites the initials FLD and VTL as action signals, referring to the 1973 course. It neither expands FLD nor specifies the three constructions and their offsets. Those details were checked in David Hickson / Sentient Trader’s later documentation and are not attributed here to the 1970 book; the original Cycles Course has not been verified in full.
Prerequisites
Phasing analysis, cycle period and underlying trend.
Definition
In plain terms — An FLD retains the shape of a price series and moves it to the right. Its offset is about half the cycle's wavelength, but the documented convention changes by one bar according to the series and use.
For a wavelength P measured in bars, Sentient Trader's post-Hurst documentation distinguishes three FLDs:
| Variant | Shifted series | Offset | Documented use |
|---|---|---|---|
| Median-FLD | (High + Low) / 2 |
⌊P / 2⌋ + 1 bars |
Confirm troughs and peaks after the bar is complete |
| High-FLD | High | ⌊P / 2⌋ bars |
Immediate buy action signal |
| Low-FLD | Low | ⌊P / 2⌋ bars |
Immediate sell action signal |
Here “median” means the midpoint of the bar's high and low, not the median of a rolling price window. The FLD level on the current bar comes from a past bar: what requires the close is the current median price being compared with that level. An immediate high/low signal does not amount to a completed median-FLD confirmation.
Example — With P = 20, the median-FLD uses an 11-bar offset, while the high- and low-FLDs use 10. With P = 21, the offsets remain 11 and 10 respectively because the half-wavelength is truncated.
Which bar am I using?
Given the series x and offset d from the table, the displacement is FLD(t) = x(t − d): the value from bar k is plotted at k + d. This makes the displacement explicit; it is not another historical variant.
With P = 20 and complete data through bar 100:
| On bar 100 | Input used | Last computable future point |
|---|---|---|
| Median-FLD | (High₈₉ + Low₈₉) / 2 |
Bar 111, from bar 100's median |
| High/Low-FLD | High₉₀ / Low₉₀ |
Bar 110, from bar 100's high/low |
The line can therefore extend beyond the last observed bar without knowing future prices. Data from bar 101 while it is still open would supply new provisional points at 112 for the median-FLD and 111 for the high/low-FLDs. Those data are not needed for the FLD level at 101, which uses completed bars 90 and 91 respectively. If a source bar is missing, its corresponding point is unavailable: do not fill it with later prices.
Crossings and confirmations
In plain terms — A crossing does not create a turning point. Within this framework it is used as evidence that the trough or peak assigned to the cycle has already formed.
Under the convention documented by Hickson / Sentient Trader:
- an upward crossing confirms a trough of the associated cycle;
- a downward crossing confirms a peak;
- median-FLD confirmation is evaluated with the completed bar's median price;
- high- and low-FLDs provide levels for immediate action signals.
The wavelength must come from a coherent phasing analysis. Changing P may change the offset and line; truncation does, however, leave the offsets for 20 and 21 bars identical. The computable future segment stays unchanged only with fixed data, series and offset. Recalibrating the period or revising the data may alter it. To check a historical crossing, use the period and data available then: a line redrawn afterwards does not establish that the signal was knowable in real time.
Price projection
In plain terms — The distance between a turning point and the crossing is reflected beyond the crossing. This is a model projection, not an order or a guarantee.
For an upward crossing at price C, with an observed trough at L:
Upward target = C + (C − L) = 2C − L
For a downward crossing at price C, with an observed peak at H:
Downward target = C − (H − C) = 2C − H
The Sentient Trader help describes the corresponding time projection as less accurate and suitable only as a rough guide.
Example — Trough 90, upward crossing 96: projected price 102. The calculation reflects the six points already travelled; it assigns no probability to reaching 102 and does not include trend, volatility or costs.
FLD and VTL
| Graphical VTL | FLD | |
|---|---|---|
| Construction | Straight line selected within an expected cyclic window | Shifted price series |
| Event | Break of the line | Crossing of price and line |
| Dependency | Pivots and time window | Wavelength and high/low/median series |
| Projection | Other tools in the method | Symmetry around the crossing |
In the tradition described by Hickson, FLDs and VTLs are used with phasing and longer cycles. This is an accessible post-Hurst formalisation; it does not by itself establish that every implementation detail was identical in the original course. Neither line removes false signals, dating errors or execution risk.
Limits
- It is a tool of the Hurst tradition as formalised by Hickson, not a universal empirical law.
- An incorrect period or phasing produces a miscalibrated line.
- Several cycles and trends contribute to price; the ideal wave is not the full observed series.
- A crossing is an analytical condition, not financial advice.
- Targets and timing require validation for the market, timeframe, data and costs concerned.
Common mistake — Applying round(P/2) indiscriminately to every FLD. The checked convention distinguishes truncation, the median-FLD's additional bar and high/low series for immediate signals.
Summary card
- Median-FLD: median price,
⌊P / 2⌋ + 1, completed-bar confirmation. - High/Low-FLD: high or low,
⌊P / 2⌋, immediate levels. - Projection: turning-point-to-crossing distance reflected beyond the crossing.
- Context: phasing, underlying trend and risk remain necessary.
Sources
- J. M. Hurst, “Cyclic Analysis”, Reason, May 1974, “A Complete Trading System” and reference 6 — primary source for the initials FLD and their general action-signal role; refers to the 1973 course without specifying the operational variants.
- J. M. Hurst, The Profit Magic of Stock Transaction Timing, Prentice-Hall, 1970, Ch. 4, pp. 69–85 — primary source for envelopes, the state table and VTLs; used here to delimit the book's method, not as a source for the FLD.
- David Hickson / Sentient Trader, FLD's — Future Lines of Demarcation — direct post-Hurst source for the three variants, offsets, confirmations and projections.
- David Hickson / Sentient Trader, Hurst's Trading Methodology — post-Hurst account attributing the methodology to the Cycles Course and distinguishing delayed confirmation from immediate action signals; the original course was not checked.
The two Sentient Trader pages belong to the same documentation and are not independent confirmations. The check concerns the conventions described, not their financial effectiveness.