Dimensional Calibration Check

The Dimensional Calibration Check is the terminal examination of any aperture proposed for regulated use, conducted to establish that the space a traveller enters is the space the aperture's registration claims. It is distinct from the wider practice of Dimensional Calibration — which assembles and maintains the instruments, records and precedents by which fidelity is judged — in that the Check is an event: a single sitting, at a stated hour, with a result entered in ink and a seal struck on the outcome. Provisional certification is issued on passage; full certification follows only after the aperture has held its exit-point within the tolerance of the Primary Null Standard on three consecutive appraisals overseen by the Provosts of Calibration.

The Check is authorised under Stairwell Calibration Ordinance 1-A, which subjects every aperture permitting regulated vertical transition to periodic dimensional attestation, and its procedure is set out at Annex 12 of the Manual of Dimensional Calibration (Rev. 44). It should not be confused with the preparatory sequence that precedes it: an aperture must first clear the Epistemic Alignment Check and the Axiomatic Compatibility Check before a Calibrator will unlock the shutter for measurement.

Procedure

The examining Calibrator opens by striking the aperture with the Caliper of Dimensional Constancy, an instrument that returns a reading only when it has been held level for a full count of forty. The Calibrator then traverses the aperture from both ends and records three crossings at the inner face and three at the outer. From the sixth reading the Check derives a drift coefficient; a coefficient above tolerances laid down in the Manual requires the aperture to be sealed until the next quarterly window. The practice of treating the drift coefficient as probative rather than advisory is defended in the Rev. 44 commentary on the ground that "an aperture which wanders once will wander again, and the second time it will be carrying a clerk with a full tray" (Manual of Dimensional Calibration (Rev. 44), §7.3).

The Check closes with the Notarization Check, then the Procedural Harmony Check, then the Crossreferential Stability Check, in that order; the sequence is mandatory and was the subject of a long procedural dispute with the Office of Dimensional Standards, which sought in 9,912 AT to run the Crossreferential first on the ground that it caught more errors, and was refused. The refusal is recorded in the minutes only as "the order is the order" (Provosts of Calibration, Minute 4,411).

Common causes of failure

Failures cluster. Roughly half of all failed Checks arise from apertures registered against an unstruck Primary Null Standard, a fault the calibrating contractor is expected to catch before the Check is formally opened. The rest divide between stairwells that discharge onto a floor of the same number they departed from, and stairwells whose exit lands in a different building of the same age and construction, which the Manual treats as the more serious of the two.

A standing rule of the examining floor provides that no one may carry luggage through the aperture during measurement, since the additional mass distorts the inner-face readings and cannot afterwards be separated from true drift. This applies to a satchel of papers as much as to a trunk.

The dispute over the 9,870 AT readings

The most cited failure in the Check's recorded history is the string of measurements taken during the Calibration Event of 9,870 AT, when the Office of Stairwell Calibration executed a series of dimensional inflections in Phase Beta on apertures already certified. The Provosts held that the inflections invalidated every prior reading and required re-examination of the affected stairwells; the Office replied that the inflections had been within tolerance and that the readings were sound. Both sides quote the same clause of the Manual — §7.3 on the probative weight of drift — in support of opposite positions.

"A coefficient obtained during an inflection is a coefficient of the inflection, not of the stair."

— Office of Stairwell Calibration, memorandum of 9,871 AT, appended to the Phase Beta docket

"An inflection they chose to make is not a storm. The stair did wander; the cause of the wandering is the Office's to answer for, not the Check's to excuse."

— Provosts of Calibration, reply of the same year, §2

No resolution was ever entered. The affected apertures were recertified in 9,874 AT on fresh readings taken in a quiet season, and the readings of Phase Beta remain in the register, struck through but legible. See also Gamma-7 Calibration and the Directorate of Dimensional Fidelity, whose mathematical review of the coefficients reached no conclusion on the question the Provosts and the Office were actually arguing about.

Record and appeal

Every Check is written up on a single sheet, sealed with the Calibrator's mark and countersigned by a witness drawn from the nearest Scriptorium. Once countersigned, a failed Check cannot be reopened on the aperture it examined, though the aperture itself may be presented again after a further quarter. A Refusal of the seal — a discretionary act available to the countersigning witness — suspends the result until a Conflict Check is held, a route said to be taken less often than the disputes it would resolve.

Discrepancies between the Check's findings and the authoritative record of a space are reconciled through Calibration proper, and the standing instruction to the examining floors is to record what the Caliper returns even where the aperture plainly disagrees with the manual. The Tower tolerates a lengthy account of the instrument's misbehaviour; it does not tolerate a shortened one.