79. For metrical purposes

For metrical purposes, syllables (not vowels) are distinguished by the grammarians as heavy (guru) or light (laghu). A syllable is heavy if its vowel is long, or short and followed by more than one consonant (“long by position”). Anusvāra and visarga count as full consonants in making heavy syllable. The last syllable of a pāda (primary division of a verse) is reckoned as either heavy or light.

a. The distinction in terms between the difference of long and short in vowel-sound and that of heavy and light in syllable-construction is valuable and should be observed.