The metre of Homer and Virgil: SIX feet, each either a DACTYL (long-short-short) or a SPONDEE (long-long). Both fill the same beat — four morae of time — so a line can have 13 to 17 syllables yet always the same duration. The fifth foot is almost always a dactyl; the last is clipped to two. Slide to swap dactyls for spondees and watch the syllables change while the beat holds.
Dactylic hexameter is six feet; a foot is a DACTYL (—≮≮, one long + two short) or a SPONDEE (——, two long). Both last four MORAE (a long = 2 morae, a short = 1), so every valid line runs exactly 6×4 = 24 morae of time regardless of syllable count (13–17). Convention fixes foot 5 as a dactyl and foot 6 as a two-syllable close. A fail-loud self-check throws unless every dactyl/spondee combination totals 24 morae across 6 feet. ◆ the metrical rule is exact, node-verified.
Foot counts and morae are exact; scanning a REAL line (deciding each syllable’s length by nature and position) can be contested at the margins — that ambiguity is the scholar’s, not the arithmetic’s.