The Aperture Test

The Aperture Test is the collective name for the family of examinations by which the Tower determines whether a bounded opening in its fabric — a doorframe, a hatch, a window, a stairwell mouth, or any of the less easily described gaps that occur between floors — conforms to the aperture categories set out in Concordance III and its successors. It is not a single proceeding. The Test comprises the photometric strand, the material strand, and the tolerance strand, which are conducted in that order and are not permitted to share a single sheet of paper between them.

The Test is administered under the standing authority of the Office of Aperture Standards, whose seal has not changed since the recension of 34 Aperture.

Origin and the warmth test

The earliest form of the Aperture Test was the warmth test, which has been in continuous use since at least the recension of 34 Aperture and which survives, largely unaltered, as the concluding step of the tolerance strand. A candidate aperture is closed, warmed from the corridor side, and examined for leakage. An aperture that admits warmth but no light is recorded as a Class II opening and is considered ordinary. One that admits neither is Class I. One that admits both is recorded, marked with a chalk cross, and referred to the Bureau of Misplaced Exits without further testing, this being the oldest standing instruction in the Office and the only one never amended.

The warmth test was extended to gloved examination by Ordinary 44, which requires the testing hand to be linen-wrapped and forbids the bare hand from contact with any aperture under examination, on the ground that a bare hand warms the frame unevenly and has produced at least three erroneous Class II findings since the practice was curtailed.

The photometric strand

The photometric strand is the portion of the Test with the most settled apparatus. A Reading Lamp, Standard Aperture, of the third pattern, is placed at the marked threshold of the aperture and screened to a single wick. A leaf of Tenebrous Paper is then presented at the far face. The paper should show no scalloping. Scalloping — a regular lobed darkening at the margin — indicates an aperture whose specification is uncertain, and the specimen is remeasured against the Standardized Gauge, a calibrated brass plate of nine apertures, to establish which of the nine categories the opening most nearly resembles.

The Gauge is held to be authoritative in all cases except where its ninth aperture is involved, which has been under seal since the dispute of the Ninth Aperture Commission and is not to be used.

The material strand and MAP-3

Where the photometric strand yields a Category of uncertain specification, the medium through which the aperture is recorded is itself tested. All suspected impermanent media undergo the MAP-3 for classification, and it is a fixed rule of the strand that a holding which resists analysis in proportion to its stated density is not passed forward. The Test's use of MAP-3 is a modified form, conducted under the Containment Strand of the Tripartite Test of Inherency, and is designed to verify only that the archival medium will accept an entry regarding the aperture, not that the entry is true.

The distinction is not academic. In the winter of the year recorded as Floor 812, the winter of the mislaid frame, a clerk of the third scriptorium, Clerk Anselm Vey, tested a service hatch on Floor 812 and found it materially consistent with the medium of record. The hatch was entered accordingly. It was later established that no hatch existed at that position, and that Vey had tested the frame of a cupboard. The Office's ruling on the matter — Ruling 19 — held that Vey had committed no error, since the material strand has never been required to attest the corridor. It required only that he be transferred, which he was, to the Registry of Unattested Corridors, where he remains.

Precedence and the question of sequence

Disagreement persists over whether the tolerance strand may be attempted before the photometric strand has returned a result. Concordance XI, Annex 2, holds that the strands are concurrent and that any order is permissible provided all three are completed within the same quarter. Concordance XIV, Annex 6, holds the opposite, insisting on strict sequence and providing that a toleranced aperture which has not been photometrically examined is to be closed and resealed pending re-test.

The Office of Aperture Standards applies the Test of Elevation in such disputes when amendment dates cannot be reliably distinguished, which in this case they cannot: both annexes are dated to the same quarter and bear seals of the same pattern. The Office has twice elevated Annex 2 and once Annex 6, and has recorded that it does not consider itself bound by its previous elevations. The Corroborative Review of the matter remains open.

"The Test does not establish that an aperture is real. It establishes that the aperture has been tested, which is the only claim the Tower has ever made of anything."

— Tenet VII, reading note appended by the Office of Aperture Standards

Tolerance strand and admission

The tolerance strand is administered at Aperture Kappa-7, where candidates for the Archivist Kappa series are examined, and it is here that the Aperture Test and the Test of Continuity are deliberately kept apart. The strict isolation of search teams, required to satisfy the Tripartite Test of Inherency, is designed so that no candidate may observe two apertures in the same session and compare them. Comparison is reserved to the Fourth Spiral Reservoir, and the drills conducted there under the Simultaneous Referential Collapse Drills are not part of the Test.

It is worth noting for the guidance of visiting readers that the Aperture Test may not be administered on a floor that is currently the subject of an open Test of Recency. Visitors are asked not to carry chalk between floors.

Inventory of strand apparatus

The Office maintains the following on standing issue to each testing party, and no other equipment is to be introduced into the examination room:

• One Reading Lamp, Standard Aperture, third pattern, screened
• Twelve leaves of Tenebrous Paper, in a sealed wallet
• One Standardized Gauge, nine apertures, aperture nine sealed
• One pair linen gloves, tested to Ordinary 44
• One chalk, white, for Class III markings only