Spatial Fluctuation

Spatial Fluctuation is the displacement, dilation, or reduction of a measured extent within the Tower without any corresponding movement of the objects that define that extent. It is distinguished from ordinary settling, from subsidence of the older shaft-walls, and from the deliberate re-surveying of a zone by Spatial Demarcation, in that nothing in a fluctuation has moved: the floor has simply become longer. The phenomenon is catalogued under Class Ψ: Metric Inconstancy and is the standing concern of Division V: Spatial and Topological Incoherencies, which maintains the register of affected zones and is the office to which all fluctuation reports are ultimately addressed, whether or not they were meant for it.

Fluctuation is measured in amplitude, expressed in chained spans, by comparison of a zone's present extent against its recorded mean volumetric state in the Master Floor Plan. Amplitudes below one-quarter span are recorded and not acted upon. Amplitudes above four spans require the evacuation of the affected galleries and a notice posted at both approaches to the floor.

History of the register

Fluctuation was first recorded as a distinct class of event in the winter of 512 S.R., when a duty Correspondent named Arlo Vex logged an anomaly at the Axiomatic Nullpoint in Sub-Sector Gamma and was obliged to append the phrase extent not as surveyed, articles unmoved to his standard report form. The form had no field for this. Vex is reported to have carried the matter upward for eleven years before Division V: Spatial and Topological Incoherencies accepted that a fluctuation might be a thing in itself rather than a failure in the survey.

The Crisis of the Unmoored Stacks (709–711 S.R.) remains the largest fluctuation event on record: seven entire wings of metaphorically-indexed holdings drifted in both meaning and extent, and three galleries were later recovered in the wrong sector, intact and correctly shelved. Since that event all wings of metaphorical holdings are re-measured at intervals of four years, and the measurements are filed whether or not they change.

The question of the cause

The cause of fluctuation is not agreed. The Fifth Concordance, Annex 2, attributes it to the non-commutative refraction of sightlines at floor junctions and defines acceptable amplitude parameters for the Ambivalent Prism on that basis. The Second Concordance, however, treats fluctuation as a species of wear and assigns responsibility for it to whichever office last certified the zone.

"A zone found in fluctuation shall be read as a zone found worn, and the office of its last certification shall answer for the wear in the manner of a debt."

— Second Concordance, Annex 7, clause 3

This clause has never been repealed and is cited roughly twice a decade, always by an office attempting to transfer the cost of a survey to another office. The Office of Spatial Reconciliation maintains a standing objection to it, on the grounds that it makes the certifier the author of the fluctuation, which the Office has called "a reading no instrument supports" in its memorial of 744.

Fluctuation and the Prism

The narrow class of fluctuation occurring at apertures is better understood than the general case, chiefly because it repeats. The Fifth Concordance formalised the procedure for measuring such events, and the parameters it sets out remain in force for all prism work. A complication arose in 903 S.R., when the duty officer of Refinery Σ-18 reported that the Refinery's measurement aperture had itself drifted eight spans north over a period of nineteen days, so that every subsequent reading of the Prism was taken from the wrong place. The readings were not invalidated; they were re-referenced, and a note was entered in the aperture's own file.

Facilities that handle volatile materials are the more carefully watched for this reason. Silentium Resin, which is synthesised only at the Vertical Refinery, is now measured at two fixed points that are checked against the Master Floor Plan before each pour. The check is recorded by the pourer. It takes about a minute.

Fluctuation Floor 44

Fluctuation Floor 44 is not, despite appearances, named for the phenomenon; the name predates the register by some two centuries and its original sense is unknown. The floor is nevertheless the Tower's most closely surveyed zone, having lost the argument over its own extent in 866 S.R., when two survey parties returned conflicting measurements and the resulting Second Survey Crisis occupied the Bureau of Spatial and Temporal Alignment for six years. The resolution — that neither party had erred, the floor having performed a Pulsatory Expansion/Contraction between the two surveys — is regarded as the founding precedent of the field.

The Ambulatory Chancery on the same floor has been asked on four occasions to move its chambers in order to avoid a fluctuation corridor, and has refused on each, citing its nine-year removal cycle as the sole authority for its movements. Its southern wall has stood in an active corridor since 891.

Reporting and known incidents

Fluctuation is reported on Form 12-Gamma through the nearest Correspondent, who forwards it to Division V: Spatial and Topological Incoherencies, which copies it to the Office of Spatial Integrity and, where light is involved, to the Office of Luminous Compliance. The Office of Luminous Compliance acquired its place on the circulation list in 788 S.R. after the captured moonlight in the Third Atrium began fluctuating on a cycle no one could predict, and its office was the only one already keeping the necessary records.

The Quarterly Spatial Forecasts carry a predicted amplitude for each certified zone and are consulted before any works are scheduled. A forecast that proves wrong is not withdrawn; a corrected forecast is issued alongside it, and both are retained. The archive currently holds 1,104 forecasts and 1,093 corrections. Some frequently noted incidents:

• The Axiomatic Nullpoint anomaly, Sub-Sector Gamma, winter 512 S.R. — the first recorded fluctuation.
• Zones of Specified Instability, Annex C: eleven galleries reclassified after the Crisis of the Unmoored Stacks.
• The measurement-aperture drift at Refinery Σ-18, 903 S.R. — eight spans over nineteen days.
• The corridor at Spatial-Topological Gaps, section 4, which has widened by one span in each of the last thirty years and is expected to require reclassification in 1,041.

Where a fluctuation is found to have altered the extent of a record room, the room's holdings are counted, but not re-measured, unless the count itself has changed.