True Azimuth

True Azimuth is the designation given to the corrected bearing at which a radial measurement is held to terminate, after adjustment for drift, jurisdictional variance, and the residual error known as stairhead precession. It is not, strictly speaking, a direction. The Third Concordance, Clause 7.02, defines True Azimuth as "the azimuth a surveyor would report if the surveyor were correct," a formulation the Guild of Scribes and Formalists has defended unaltered for four amendments and one attempted repeal.

True Azimuth is maintained in the Master Registers of Azimuth and Length and is admitted as evidence in disputes only when certified against the current True Inch. The two units are calibrated independently and reconciled quarterly under the Quarterly Registry Reconciliation Schedule, a process that has not concluded cleanly since its introduction.

Definition and derivation

An observed bearing is reduced to True Azimuth in three stages. First, the reading is corrected for Stairhead Drift, the cumulative angling of floor plates relative to the plumb line, measured at 0.6 degrees per hundred floors in the eastern shaft and not measured elsewhere. Second, the reading is adjusted to the nearest registered figure in the Master Registers of Azimuth and Length, which are held to be authoritative regardless of what the instrument reports. Third, the result is certified by a Cantor of the Cantors of the True Inch under Clause 4.19, on the grounds that a bearing is only as true as the length against which it is plotted.

The third stage is the one most often disputed, and it is the reason no True Azimuth may be reported by a single surveyor. Standard Practice Notice 88 requires two certifying officers and one witness, none of whom may have stood on the same landing during the preceding year.

The Lysander controversy

Between the 412th and 419th reconciliations, the Ephemera Wing supplied surveyors with a prepared medium it marketed as Lysander Parch, warranted to hold a plotted bearing without creep. Bearings plotted on Lysander Parch were found to drift by up to four degrees over a single shift, and the resulting figures were entered into the Registers without correction.

The consequence is the Lysander Anomaly: a wedge of floor sectors, chiefly between Floor 909 and Floor 1140, in which every recorded True Azimuth is held to be wrong by a known but unpublished amount. The Ephemera Wing has argued that the parchment recorded the bearing truly and that the Registers were at fault for preferring their own figures. The Guild of Scribes and Formalists has declined to rule, noting only that the Wing was formally established as the sole authorized producer of true Lysander Parch and that this establishment was never rescinded.

Since 421, all bearings in the affected sectors have been carried forward by extrapolation rather than re-observation. Extrapolation is performed by the Office of Carried Bearings, whose staff have not visited the sectors in question.

Scholarly disagreement

The Materialist School holds that True Azimuth is simply the bearing obtained by careful work with a sound instrument, and that the term "true" is a courtesy extended to competent surveyors. Its position paper, On the Sufficiency of Careful Work, argues that certification adds nothing to a reading taken by someone who knows what they are doing.

The Realist School rejects this entirely. On its account, True Azimuth must be absolute and immutable, and a bearing that varies with the observer's care is not an azimuth at all but a preference. Ardis Vole has argued, in the Vole Commentary on Clause 7.02, that the Realist position requires True Azimuth to be knowable in principle and never in practice, which he regards as a feature rather than a defect.

The Null Collective is not party to the dispute, having withdrawn on the grounds that any accredited bearing is by definition not null and therefore not worth discussing. The Lira of the Forty-Seventh Landing has separately argued that since the number of Interstitial Landings is incalculable, no bearing can be closed to a known point, and that True Azimuth is consequently a figure of speech preserved by administrative habit. The Lira's argument is widely cited and never adopted.

Contradiction between instruments

Concordance 12, Annex D, requires that True Azimuth be reported to four decimal places. The Second Concordance, which was never formally superseded on this point, requires whole degrees and forbids the recording of fractions on the grounds that they invite dispute. Both remain in force. The Vault of Conditional Forms holds 1,408 completed forms in which both requirements were satisfied by entering the fractional part in a separate column labelled "remarks."

"Where two instruments return different True Azimuths to the same point, the elder instrument governs, unless the elder instrument has been recalibrated, in which case no instrument governs and the matter is referred."

— Third Concordance, Clause 7.19

Referral under Clause 7.19 is made to the Committee on Unresolved Bearings, which has not issued a determination since its formation. Its minutes are regular, brief, and identical.

Use in practice

True Azimuth is required for the siting of new shelving, the orientation of Provisional Instrumentals, the plotting of resonance packet receptions, and any movement between floors on which the Pre-Dawn Evacuation order is expected to apply. Surveyors working from a certified True Azimuth are indemnified against loss of footing; those working from an observed bearing are not.

The distinction is taught in the first week of instruction and misunderstood thereafter. The School of Fixed Points offers a remedial course, Azimuth: The Difference, which runs for eleven sessions and concludes that the difference cannot be taught.