Aperture Phases

Aperture Phases are the discrete intervals into which the Tower divides the opening, holding, and closing of its apertures, and the periods of observation that attend each. The term is used in two senses that the archive has never fully separated: the operational sense, in which a phase is a state of an aperture, and the administrative sense, in which a phase is the paperwork that a state of an aperture obliges. Disputes over which sense is primary have occupied the Iterative Chamber for the better part of two centuries and are unlikely to be resolved in this one.

Origin and Standardization

Aperture Phases were first reduced to a single schedule by Curator Vael, the first Lead Surveyor for Aperture Phases, whose survey notebooks (held at Floor 214, Spiral C) record eleven competing phase-counts in use among survey teams before her reforms. Vael settled on a working set of phases and, more durably, on the practice of recording a phase only after it had ended, on the grounds that a phase recorded while in progress was "a phase of the recorder's uncertainty rather than of the aperture" (Vael, Survey Notebooks, vol. 6, fol. 41). The practice survives; the phase-count does not, having been amended nine times.

The governing text is the Third Concordance, whose Clause 14 assigns phase authority to the office of the Lead Surveyor and whose Annex Delta sets out the seven sequential phases of measurement applied whenever an aperture's condition is inventoried. Clause 14 and Annex Delta are not in agreement on whether a phase begins at the moment of instruction or at the moment of measurement; the discrepancy is known as the Aperture Interval and is discussed below.

The Phase Sequence

In the operational sense, an aperture passes through an opening phase, a holding phase, and a closing phase, with an interstitial phase between each. The interstitial phases were introduced by the Seventh Concordance and were not accompanied by any provision for their termination, a defect that produced the so-called Long Interstice of Floor 88, during which an aperture remained interstitial for four years and eleven months while three successive survey teams measured it, recorded that it had not changed, and were reassigned.

The sequence is not to be confused with the Ventilation Phases, which are six in number, are defined by non-acoustic resonance patterns and pressure differentials, and are administered separately by the Ventilation Chorus under the Seventh Concordance's annexes. The confusion is nonetheless constant. In the winter of 1041, a survey party on Floor 331 recorded a full aperture phase sequence for a doorway that proved, on inspection, to be a ventilation return. The party's report was not withdrawn; it was reclassified, and the incident is cited in every subsequent edition of the surveyor's handbook as an example of what the handbook calls "a persuasive draught."

The Aperture Interval

The Aperture Interval is the period between the instruction to measure an aperture and the measurement itself. It is, in principle, instantaneous. In practice it is subject to the clerical deployment schedule of the measuring office, which runs to five phases of its own, and the two sequences are not synchronized. Commissioner Aris Thorne proposed in 988 that the Aperture Interval be abolished by measuring first and instructing afterwards; the proposal was carried, attempted on Floor 12-β, and withdrawn after eleven days. No record of what occurred during those eleven days was retained, and the Commissioner's later note on the subject consists of a single sentence: "The interval is load-bearing."

"Where the instruction precedes the measurement by more than the holding phase, the aperture is to be regarded as having opened in the absence of any observer, and the phase is to be recorded as unattended, in the form prescribed."

— Third Concordance, Annex Delta, para. 9

Observation and the Horticultural Threshold

Because phases are recorded after the fact, the light reaching an aperture during a phase is often the only contemporaneous evidence of what that phase was. Cultivar Standard 114-Δ-7b, enforced by the Directorate of Horticultural Chronometry, fixes light-intensity thresholds for each phase of the Aperture Cycle and requires that any aperture under cultivation be inspected at phase boundaries. The Standard has been amended twice, both times to accommodate apertures that were not under cultivation but had been recorded as though they were.

Practical guidance is sparse and jealously guarded. The surveyor's handbook states, without elaboration, that no phase is to be recorded during a meal, and that an aperture found open at the change of shift is the responsibility of the outgoing shift.

Scholarly Disagreement

The Guild of Procedural Archivists holds that procedural phases are ontologically primary — that the aperture's opening is a consequence of the phase rather than the reverse — and cites the Third Concordance's ordering of instruction before measurement as evidence. Against this, the School of Ephemeral Cataloguing maintains that phases are retroactive descriptions with no existence outside the record, and that the Long Interstice was not a duration but a filing error. The Iterative Chamber has declined to rule, noting in its quarterly report of 1044 that the question "lies beyond the Chamber's phase."

Where the parties agree, they agree on procedure. Under the Provisional Concordance Citations regime, a phase recorded without a citation may be cited provisionally for up to one year, after which it lapses and the aperture must be measured again. It is not permitted to cite a lapsed phase in support of a new one.

Recorded Phases of Note

• Floor 9, First Aperture — holding phase of nineteen years; still holding.
• Floor 88 — Long Interstice, 1036–1041; closed by administrative order, not by measurement.
• Aperture 12-β — Interval attempt, 988; eleven days, no record.
• Floor 331 — ventilation return recorded as full phase sequence, winter 1041; report reclassified.
• Aperture 303 — phases recorded in reverse order for six years; the error was not detected because the reverse order is also a permitted sequence.