Māṇḍūkī Śikṣā 116

116

mātraikaṃ laghu vijñeyaṃ tatsaṃyogaparaṃ gurum
sa paraṃ vyañjanāntaṃ ca dīrghastu pluta eva ca

One mora is to be known as light; that which precedes a conjunct is heavy; / that which follows it and ends in a consonant is [heavy], as are long and protracted.