Lamp of the Determination of Lunar Days

If the Third Lunar Day Tritiya is joined in the [latter] portion and is not "pierced" viddha original: "viddhā"; a technical term for a lunar day that is considered "contaminated" because it overlaps with the sunrise of the preceding day, then it is considered pure for rituals here as well. || 28 || For the commencement of a vow or similar ritual, the calculation follows this: if the day covers the midday madhyahna-vyapini original: "madhyāhnavyāpinī"; the period around solar noon, considered critical for many Hindu rituals, that day alone should be accepted. The Fourth Lunar Day Chaturthi may be taken as the preceding day, or otherwise the following day, depending on specific conditions. || 29 ||

If the Tithi a lunar day is found on both days [the preceding and the subsequent], then based on the equality or inequality of its duration on those days, the earlier one is selected due to its proximity. || 30 || If only the later day covers the midday period, then that later day alone is the one to be taken. This is the settled determination for the calculation of the Fourth Day Chaturthi regarding the start of vows and other rites. || 31 ||

Even in the case of the Serpent Vow Naga-vrata original: "nāgavrate"; a ritual fast and worship dedicated to the serpent deities (Nagas), usually performed on the fourth or fifth day of the lunar month, the wise do not strictly insist on the midday coverage. The decision remains whether the Fourth Day should be the earlier one or the later one. || 32 || If the Tithi is present on both days, then through the comparison of equality or inequality, the later day is chosen if the proximity favors the subsequent time. || 33 || If only the earlier day covers the midday, the Fourth Day that provides the correct timing is the earlier one; in that case, the earlier day must be accepted, and the later day should not be taken.