Reference
The guides show how to measure something. This section answers the three questions that come after: why is the formula this one, is the implementation actually right, and where does it come from. Nothing here is a tutorial, so nothing here has to be read in order; these are pages to arrive at from a guide, from a report you are writing, or from a reviewer’s question.
Use it when you are defending a result rather than producing one. If a colleague asks which clause of ISO 3382-1 the reverberation time follows, the theory pages say so; if a client asks for evidence that the library computes it correctly, the conformance report shows the standard’s own expected value next to the computed one; if a journal asks for the source of a model, the bibliography has the DOI.
If you are only looking for the signature of a function, you want the API reference instead: it is generated from the source docstrings and lives in its own section of the sidebar.
The standards, the mathematics and the design decisions behind every module, in six domain pages: signal analysis, perception and hearing, rooms and buildings, materials and surfaces, environment and transport, and vibration. Start here when a guide states a result and you want the derivation, the clause it implements, or the reason one formulation was chosen over another. The theory for the underwater modules is the exception: it lives inline with its guides.
The numerical evidence. Every check names a standard, a clause or table, the normative expected value, the value the library computes, the delta and a pass/fail verdict. It is regenerated and enforced by CI on every pull request, so it describes the code as it is now rather than as it was documented once. Read it when you need to show that a number is defensible, or to see exactly which parts of a standard are implemented and which are not.
The other side of the same coin. Re-deriving every formula and worked example from the source document occasionally shows that the document is wrong: an example that contradicts its own normative clause, a misprinted constant, a cross-reference pointing at the wrong equation. Each confirmed case is recorded with the printed edition, the evidence, the reading the library implements and the test that pins it. Read it when a printed expected value and the library disagree, before assuming the library is at fault.
Every book and paper cited by the guides, in one list grouped by domain, each entry with a verified DOI or official publisher link, half a sentence on what it supports, and the guide pages that cite it. It doubles as a reading list for the field and as the single source of truth for link checking.