Standard Chronon

The Standard Chronon is a Primary Instrumental housed in the Vault of Primary Measures, where it serves as the Tower's standard of temporal duration. It should not be confused with the Tower Standard Chronon, which is a unit; the Standard Chronon is the object against which that unit is periodically verified. The distinction is maintained in ordinary speech by referring to the instrument as "the Chronon" and to the unit as "the chronon," though in writing the difference is carried only by the capital letter, a convention that has caused no small amount of litigation.

The instrument stands on a plinth of Folded Time Alloy at the north end of the Vault, separated from the Prototypical Cubit by a partition of the same alloy, which is held to prevent the two measures from keeping one another company. Whether they would do so if unseparated has never been tested, and the partition is inspected every eleven years by a party of two Librarians who are forbidden to speak while inside it.

Description and operation

The Standard Chronon is a sealed column of dark masonry, 2.4 Standard Brackets in height and 41 Standard Lumens in circumference, containing a single suspended mass that is said to advance by one discrete interval at each completed oscillation of the Series of Standard Intervals resonators housed in the adjoining chamber. The mass is not visible. Its advance is inferred from the behaviour of the instruments that depend on it, a method the Office of Standard Tower Units has defended since at least the tenure of Archivist Velden Marrow, who observed that "a clock one cannot see is a clock one cannot argue with" (Marrow, Notes on Difficult Measures, floor 8,811).

Calibration is performed against the Standard Temporal Unit: a full reading of the Chronon comprises 86,400 Standard Temporal Units, the same figure by which the Tower Standard Chronon is defined, and the coincidence is regarded as evidence that the instrument is working. When the figures diverge, the Office holds, the instrument is at fault and the unit is not.

The recalibration of Year 14,322

The Chronon's record is unremarkable except for the winter of Tower Standard Year 14,322, when a draft through the north aperture was found to have advanced the suspended mass by an interval later estimated at between four and nine chronons. The Standard Floor Units Controversy was at its height that season, and the discrepancy was seized upon by parties on both sides before anyone had thought to check the aperture.

The Vault was closed for eleven days. A junior clerk of the Office, Seppeline Ard, was tasked with drafting the incident notice and produced a document of such thoroughness — forty pages, with a fold-out diagram of the draft path — that it was entered into the Standard Tower Chronology entire. Ard's notice contains the only formal prohibition arising from the affair: "No member of the inspection party is to leave the north door ajar, however briefly, on the grounds that it has been briefly left ajar before" (Incident Notice 14,322/4, Annex B). The door has been left ajar twice since.

Scholarly disagreement

Two Concordances govern the Chronon and do not agree. Third Concordance, Annex 4, holds that the instrument is authoritative in itself and that the unit is derived from it — "the measure follows the measured thing, as the shadow follows the stone." Ninth Concordance, Article 2, reverses the relation, declaring the instrument a "servant of the standard" and providing that any reading of the Chronon at variance with the Tower Standard Chronon is to be corrected rather than recorded. The Office has adopted the practice of recording the variance and correcting the reading, which satisfies neither document and has done so for sixty-one years.

"Where two Concordances speak to one instrument, the instrument is to be kept wound and both Concordances shelved together, so that the disagreement may be consulted in one place."

— SP, clause 19

A minority position, advanced by the Guild of Instrumental Copyists and rejected four times, proposes that the Standard Chronon be duplicated so that each Concordance might have its own. The Office has replied, consistently and without elaboration, that there is one Vault.

Relation to the Standard Chronon units

The instrument is the reference for the Tower Standard Chronon, the Standard Chronon of ordinary commercial use, and — through the resonators — the subdivisions tabulated in the Series of Standard Intervals. A divergence of ten percent from the Tower Standard Chronon along a specified axis is defined as one Standard Drift Unit, a measure used chiefly to describe the Chronon's own deviations, which have never approached that figure. The Standard Lumen and the Standard Bracket are verified in the same Vault, though on the south side of the partition, and the two parties of verifiers take their breaks at different hours by long arrangement.

Access and maintenance

The Standard Chronon may be viewed by any holder of a Standard Topographical Index entry for floor 0, on the second and fourth rest days, for a period not exceeding the time required to walk its circumference at an unhurried pace. Instruments of any kind are surrendered at the door. The plinth is dusted on the first rest day of each month; the duster is kept in the south cabinet.