A length is a specified pair of events
A moving rod’s length uses endpoint positions measured at the same time in the measuring frame. Transforming a pair simultaneous in another frame usually does not produce that measurement.
Read · Special relativity: from clock operations to electrodynamics · Results
§2 · lengths and measurement events
Follow the introduction and all ten sections, including field transformations, finite light complexes, moving mirrors, charge-current transformations, and the electron-force conventions.
Newly authored explanatory preview in modern notation, with editorial and physics review pending. Both the kinematic and electrodynamic halves are treated, but this is not a German transcription, an aligned translation, or a complete critical edition. The source paragraphs, footnotes, acknowledgment, and date-lines are not claimed to be fully represented or reviewed here. Headings and argument units are editorial.