Ludlow Unit

The Ludlow Unit (abbreviated Ld) is the Tower's principal measure of cognitive dampening, defined as the attenuation in noetic transmission produced by one Standard Tower Unit of Mindfelt Padding under conditions of full actualization. It is the working unit of the Office of Acoustic and Noetic Harmony, which first defined it, and the reference scale against which the Ventilation Division conducts its routine corridor inspections. Owing to the indirect relationship between padding efficacy and structural behaviour, the Ludlow Unit has also become the accepted proxy for the load-bearing capacity of noetic supports, a use its framers did not intend and have twice attempted, without success, to prohibit.

Definition and derivation

The unit is defined by calibration rather than by first principles. A reference specimen of Mindfelt Padding, held in the Office's sealed cabinet on the eleventh gallery of Central Foliate, is applied to a corridor segment of known Standard Tower Unit length and subjected to a standard noetic load. The resulting deflection, corrected for temperature and for the Standard Lumen Unit readings taken at both ends of the segment, yields one Ludlow Unit. The definition assumes a corridor of uniform circular section and a subject in full actualization; departures from either condition are handled by the correction tables in the Office's Provisional Handbook of Noetic Mensuration, which has been provisional since its third recension.

Because the scale is logarithmic above 40 Ld, an increase of one unit represents a tenfold reduction in transmitted thought rather than an additive one. Clerks who forget this are the single largest source of error in the annual returns. The Office's standing notice on the subject, posted at every calibration station, reads in full: "Above forty, count carefully."

Relationship to the Kael Unit

The Ludlow Unit is frequently confused with the Kael Unit, which measures Narrative Inertia rather than dampening. The two are not convertible, although a working approximation of 1 KU to 3.2 Ld is permitted for corridor surveys under Fifth Concordance, Annex 9. That annex was drafted for a single season's surveys on the western spirals and has never been withdrawn. The Office has sought its repeal at four successive sittings of the Concordance Committee, arguing that the approximation fails badly on floors where narrative load is high and padding ancient. The Ventilation Consortium opposes repeal, noting that the approximation is the only figure its inspectors can apply without returning to Central Foliate for calibration.

Dispute over the baseline

A persistent scholarly disagreement concerns whether the Ludlow Unit should be referred to a dummy subject or to an actualized one. The Office's founding definition, recorded in its instrument of 3 Ember 41, specifies "a subject fully actualized and in possession of its own name." A rival reading, advanced by the Scriptorium of Weights and supported by a minority of the Office's own calibrators, holds that the original instrument intended a dummy, and that the words were altered during transcription by a copyist who had been working from a draft annotated in the margin.

"The Unit is what the cabinet yields. Where the cabinet and the commentary disagree, the cabinet is to be preferred."

— Office of Acoustic and Noetic Harmony, Ruling on the Baseline Question, clause 6

The Scriptorium has not accepted the ruling and continues to publish its calibrations on the dummy basis, in a separate series marked with a dagger. Both series are accepted for filing. Neither is accepted by the other.

The Marrow Lane incident

In the winter of the year 78, a survey team on Marrow Lane recorded a corridor reading of 112 Ld, a value the scale was not then thought to permit. The team's clerk, Ondrej Vasp, filed the return with a marginal note observing that the padding in question had been installed in the previous decade and could not plausibly exceed 60 Ld. His note was struck from the filed copy as impertinent, and the reading stood for eleven years.

The figure was eventually traced to a draught in the calibration cabinet, which had been left ajar by a junior calibrator during a shift change. The corrected reading was 54 Ld. Vasp, by then retired, was invited to witness the correction and declined in writing, observing that his note had been struck from the filed copy. The cabinet has since been fitted with a latch. Nothing else about the procedure was altered.

Use in enforcement

The Ventilation Division enforces padding thickness and Ludlow saturation under the day-to-day authority of the Consortium. Saturation is recorded at each corridor mouth on a card, in Ld, to one decimal place. Cards recording a saturation above 70 Ld are forwarded to Central Foliate for review; cards recording a saturation below 12 Ld are also forwarded, for a different reason. Cards between those figures are filed and not read.

Inspectors carry a small brass rule graduated in Standard Tower Units and are required to measure the padding themselves rather than accept a posted figure. The rule is not graduated in Ludlow Units, and no instrument capable of reading them in the corridor has ever been issued. Asked about the discrepancy, the Division's standing reply is that the Ludlow reading is a judgement, not a measurement, and that judgements are made at the desk.

Current status

The Ludlow Unit remains in force, unamended, alongside the daggered series and the permitted Kael approximation. A proposal to decimalize the scale was referred to the Concordance Committee in the year 96 and has not been returned. The reference specimen in the cabinet on the eleventh gallery is due for replacement in the year 112; the replacement has been ordered, and the order has been acknowledged.