Four kinds of evidence, one rule
A fact is committed only with a source: a document page and region, a spreadsheet cell, a time range of meter data, or a site observation. Nothing else is accepted.
Page
p.3 · region · verbatim text
Cell
Sheet2!D14 · formula kept
Time range
kiln_kw · 1–30 Apr · 720 rows
Observation
visit 2 · 14:32 · observer