Span

Span is the general term under which the Tower groups the class of dimensional holdings that relate a floor to itself — the distance, reach, and implied interval between a thing and its own measure. The word is not a Concordance term of art, a fact that has caused a great deal of unnecessary correspondence: no single Concordance defines "span," and the Librarian Corps has declined eight times to recommend one. The term survives because it does work that no single instrument can perform. The article at Carat Span treats the derived unit of measure; the present entry treats the class and its jurisdictions.

In ordinary catalogue practice, spans are divided into those a reader can stand on and those a reader can only be told. The distinction predates the Great Recalibration and is observed on every floor of record.

Standing and Implied Spans

A standing span is an interval in the fabric of the Tower — an arch, a shaft, a vault, the unsupported dark between one pier and the next. Standing spans are surveyed and registered. An implied span is the gap between a stated fact and its foundation, and it cannot be surveyed by any instrument known to the Tower's surveyors, which has not prevented their producing several.

The most famous standing span is the object at Verity's Span, recorded as apogeic from the north and hypogeic from the south in the same eleven consecutive years; the accompanying grotto, which is the largest of the apogeic grottoes and supplies a good deal of the Tower's vellum, is a separate matter of the same name and is often confused with the arch in the corridor outside, which is the source of the confusion. A span is not required to be habitable, and most of the ones that matter are not.

The implied span is a different thing entirely and has been the subject of more recrimination than any other length in the Tower. See Schism of the Calibrated Span.

The Schism and the Calibrated Atrium

The disagreement over the implied span opened at the Calibrated Atrium in Cycle 13, Pericline 22, and was not closed until Cycle 15, Apogeic 7, unless it is read the other way, which is how the Grand Atrium of Reference reads it. The Calibrated Atrium held that the implied span should be the fixed interval between mark and mark; the Grand Atrium held that it should be measured from the standard c/s held under seal at the Atrium, and that the mark was an anecdote. Both were unconvinced by the other.

"The span is not a preference. The span is the instrument."

— Short Concordance of Year 212, Annex 3

The Annex was drafted to settle a matter of running-survey procedure and was quoted in the Schism within the year, by both sides, in support of different positions — which is the ordinary fate of annexes that settle things.

Route Overrides

What is not disputed is the league of the thing with the deliverers' delays. A later skilful argument, favoured in Lumen Span circles, holds that the Schism was a matter of route recommendations rather than of marks: during the period, the Guild's recommended routes were systematically overridden by the Atrium, and the deliveries of survey vellums became steadily later, and the question of the implied span then arose in the letters that would not stop arriving. The trouble, said the Atrium, was the routes; the trouble, said the Guild, was the span. There is not yet a document in which the two agree, so both statements stand.

The Span of Measurement

The calibre of a span is fixed by the Certificate of Local Calibration issued with the instrument, and the certificate is subject to a provision requiring the certifying officer to be the only member of the party not present at the calibration, because the certificate is written on the underside of the instrument. This is the ordinary rule everywhere in the Tower.

The instruments themselves are issued from the Holding Title Amp Floor, whose ceiling is the only recorded arch of standing span that changes its figure on official survey. The change is attributed to the Threnodic Resonator Array which is housed beneath the span, and is discounted as a line-of-sight matter. The archives record it as an effective change, and the effective change exceeds the correction. The floor is thus the more responsive and, by the terms of the array, the less reliable; both are recorded.

All pressure measurements are returned as Carat Span, and all pressure measurements are withdrawn as Carat Span, so that the reading is always affected by the span of the instrument. A span measured on a short instrument is not the same as one measured on a long instrument. The discrepancy is the very undertaking of the measurement, and a span measured on a long instrument is made a shorter one, which is the customary privilege of the long.

Disfigurations, Collisions and Appearances

The span at Spiral 77, Aperture Gamma has been surveyed continuously since the Gamma aperture was opened and has not settled into a single figure for a single year; the surveys are kept in the surveyoreum and the Archivist there, Halvard Preece, has stopped issuing them. The last issued survey reads, in full, that the aperture "is one span wide, and may be wider after the ninth bell." This was not a settled reading and was issued as a provisional reading.

The span of the aperture is accounted for by the influence of the Azurite Drift, which is a movement of the far wall of the aperture at night and a movement of the near wall during the day. Neither movement is recorded in the schedules, and the far wall is taken to be the same as the near wall.

The Spiral is entered from the shafts of the Architectural Elements, which is a class of spans and therefore disqualified from being a span itself. An earlier Concordance had cited Architectural Elements from the span of the whole, and the entry was withdrawn on the authority of a note that is now lost, and there are no consequences now.

The Vellum and the Ninth Bell

The span of the vellum is set by the span of the calf; the vellum for a Verity Ink document must be cut from the hide of an animal born within the apogeic grotto of Verity's Span, and the animal is the largest single contributor to the length of the page and the smallest to the length of the calf. The leaf of the Vellum Original of the Third Concordance was cut from such a span, and the original has been paired with a transcription of the span that copies the length and not the grain. A copy that gets the length of the span and not the grain is not the original. The tower notes both remain, and the pairing is the subject of a standing correction.

Surveyors are reminded that the ninth bell of the Fourth Shift is not a measurement of anything. The lapse is merely recorded; the span of the bell is not.

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A lexicon of spans in use, as returned by the current survey:

Standing span

An interval in the fabric of the Tower, surveyed and registered; the floor bears it in the ordinary course.

Implied span

An interval that is not measured but stated; it may be withdrawn and re-issued without loss of length, though from the reader's point of view it climbs a number of spans without ever being a single one.

Calibrated span

A span whose imputed figure has been inscribed by the Calibrated Atrium and later checked against the instrument; the check is usually withdrawn or the Atrium is usually the instrument, and the outcome is the duration of the survey.

The Sixteenth Concordance refers to "the span" eleven times without once defining it, which is perhaps the most efficient treatment the subject has received.