सिद्धान्तशिरोमणि: गणिताध्याय (भास्कराचार्य - ग्रहगणित, मध्यमाधिकार व स्पष्टाधिकार सटीक)

27 Kshayāhas were explained before and their number in a Kalpa is the difference of the civil days and the tithis. Verses 11, 12. The numbr of solar months in a Kalpa is 51840000000; the number of lunar months is 53433300000. The number of solar months being subtracted from the number of lunations, we have the number of Adhikamāsas—The number of solar days together with the days of Adhika months are equal to the lunar days or the tithis; or again the lunar days minus the Kshayāhas are equal to the number of civil days or the reverse will be had by a reverse process. Comm. Already explained. Verse 13. The excess of the sidereal revolutions of the moon over the number of the Sun’s sidereal revolutions is equal to the number of chāndramāsas or lunations. Or again the excess of the sum of the sidereal revolu- tions of the moon and the tithis over the sum of the luna- tions and the diurnal revolutions of the stars is equal to the number of Kshayāhas. Comm. The first part is clear. Regarding the second, let the number of lunations be x and the number of the sidereal revolutions of the moon be y. Then y —x =z, the number of the sidereal revolutions of the Sun because y — z = x from the first part above. If now, the number of the diurnal revolutions of the stars be t, then t — z = t — (y — x) = t + x — y = civil days. Subtracting these civil days from ‘U’ the number of Tithis, we have the number of Kshayāhas namely U — (t + x — y) = (U + y) — (t + x) which accords with the statement. Verse 14. The number of Adhikamāsas is equal to the excess of the number of sidereal revolutions of the Moon over thirteen times the number of sidereal revolutions of the Sun.