Echo-Locus Drift

Definition

Echo-Locus Drift is the displacement of a catalogued subject's manifested position from its certified Conceptual Locus over successive measurement cycles, occurring without any corresponding amendment to the locus registry. It is distinguished from Semantic Drift and from Nominative Drift by the fact that the subject's meaning and its name both remain intact; only its location within the locus wanders. The Chamber of Measured Drift records Echo-Locus Drift in negative Standard Drift Units (SDUs), a convention inherited from the chamber's founding instrument and never revised, with the result that the larger the drift, the smaller the number that reports it.

The phenomenon was first entered in the register in the winter of Floor 1,144, when a survey party re-measuring the locus of a minor catalogued implement found it standing eleven inches to the left of its certified position and could not establish when it had moved. The implement's own records showed no movement. The locus's records showed no movement. Both were correct, and the discrepancy was filed under a new heading rather than resolved.

Mechanism and the Mercurial Standard Gauge

Echo-Locus Drift is quantified by adapting the three parameters of the Mercurial Standard Gauge. Latency is measured from the last certified placement rather than from first manifestation; Fidelity Drift is read against the subject's original Echo Crystal rather than against the current survey; and Resolution State is recorded at the moment the drift is first observed, not at the moment it is confirmed. The third substitution is the subject of continuing objection from the Office of Instrumental Reconciliation, which holds that a Resolution State taken at first observation describes the observer rather than the subject.

In practice, drift is detected through Echo-lines, which bend measurably when a locus is under displacement. A bend of less than one part in four hundred is treated as noise. A bend above that threshold obliges the surveying clerk to file a Form 12(b) and to take no further measurement that day, a rule introduced after the Floor 1,144 party took nine consecutive readings and produced nine mutually exclusive placements, all of them certified.

The Receding-Locus Question

Because Echo-Locus Drift frequently presents as a subject moving away from the instrument measuring it, early investigators confused it with the Zeno Anomaly. The two are now formally separated. In the Zeno Anomaly, the plotted vectors converge on a locus that recedes with measurement precision. In Echo-Locus Drift, the locus itself is stable and the subject departs from it. The distinction is invisible in a single reading and requires at least three, taken on separate days, by clerks who have not discussed the case.

"Where the locus recedes, the fault is in the instrument. Where the subject recedes, the fault is in the subject. Where both recede, the clerk is to set down the instruments and refer the matter to the Chamber."

— Third Concordance, Annex 4, clause 9

Clause 9 has been cited in every disputed case since its promulgation and has settled none of them, because it does not say what the clerk is to do when only the clerk recedes.

Drift-Sheen and Secondary Loci

Displaced subjects leave Drift-Sheen at their certified positions, a residue that accumulates over repeated cycles and is the principal physical evidence that Echo-Locus Drift has occurred. Sheen deposits at a locus are read in layers, like sediment, and the Registry of Lingual Drift maintains a standing comparison series of sheen profiles taken from static loci that have never drifted, for purposes of exclusion.

Where drift is small, the subject is sometimes observed to manifest at a Secondary Locus near its certified position before returning. Secondary manifestations of this kind are not counted as drift events unless they persist past the noon measurement, and the noon measurement itself is the anchor of the Dynamic Locus on Floor 7,842, which has drifted once in recorded memory and was re-anchored by Day 3 procedure at considerable expense.

Dispute: The Retroactive Reading

The Ninth Concordance holds that Echo-Locus Drift is always retroactive in character and should be classified under Retroactive Drift, on the reasoning that a subject found away from its locus was, in the registry's view, never at its locus at all. The Third Concordance disagrees, holding that drift is a forward event with a discoverable beginning, and that the retroactive reading makes the registry unfalsifiable. The Office of Instrumental Reconciliation has declined to endorse either position and continues to file under both headings, a practice the Chamber of Measured Drift has twice described in writing as "untidy" and once, in a marginal note of 2,209, as "the only honest course."

The practical consequence is that drift totals for any given floor may be consulted in two incompatible series. Both are certified. Neither is preferred. The chamber's standing instruction to visiting surveyors is to state which series they are quoting, and to state it before the number rather than after.

Anti-Drift Measures

Anti-drift measures at a locus consist chiefly of re-certification, which resets the reference position to wherever the subject now stands and records the change without explanation. Re-certification is permitted no more than four times per locus per decade; beyond that, the locus is retired and a new one consecrated nearby. Of the 1,406 retired loci in the chamber's inventory, 211 were retired without a successor, and their subjects are listed as catalogued but unplaced. They may be consulted by appointment. Visitors are asked not to stand where the subject is expected.