Clavius used Indian Maths to solve the problems of the Julian Calender !

The Tropical Zodiac precedes, roughly, 72 years per degree and this is known as the Precession of the Equinoxes.

At the time of Pope Gregory, the seasons were changing and Gregory was in a fix. He empowered Christoper Clavius to head the Gregorian Calendrical Reforms Committe. The Sine Tables of Aryabhata and Madhava were here. Also the Tan tables of Brahmagupta. A's Sine Table was the first sine table erected in the entire history of Maths, says Wikipedia.org.

http://en.wikipedia.org/wiki/Aryabhata_sine_table

http://en.wikipedia.org/wiki/Madhava%27s_sine_table

Now Clavius learnt Astronomy and Maths from the  Jewish Guru, Pedro Nunes. Clavius empowerd Matteo Ricci, to go to India, to Kerala and learn from the Time Keepers of Panchangas, to learn from the Brahmins and the Moors, this astro mathematical knowledge, which alone could solve the problem from them. 

Now Aryabhata's Sine Tables is called the Table of R Sin Differences.

R is the magic figure in Astronomy and is computed thus

PI = C./D

Pi = C/ 2 r

C = 2 Pi r

360 = 2 Pi r

r = 360/2Pi

r = 180/Pi

r = 57.3 degrees

r = 57.3*60 minutes

r = 57.3*60*60 seconds

r = 206265 seconds and this R in seconds is Known as the The Magic Figure of Astronomy.

The base of all astro algorithms for Astro Software is this R.

Bhujajya / Trijya = Opposite Side/ Hypotenuse .* R

Even though Bhujajya resembles the modern Sine , it acutally is R Sin.

Clavius. Matteo Ricci et al got access to Indian trignometric functions and inverse functions ( arcsin, arccos, arctan, cot, secant and cosecant ) and with the help of Indian Maths, (India in general and Kerala in particular) , solved the problems of the Julian Calender.

Pope Gregory had to add ten more days to the Julian Calender. Today is Oct 4 and he decreed, like God, that tomorrow is Oct 14 ! This is the so called " Gregorian Calender", which Albert Pyke, the Father of American Freemasonry called the Vulgar Era !

This is what happens when you base everything on the Tropical Zodiac, which is preceding roughly 72 years per degree. On the other hand the Sidereal Zodiac doesnt precede, as it is static.