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

307 Now let us see how the convention of signs is stipulated in Hindu astronomy with respect to the equation a = b + s. We have said that ‘s’ is always north of the East-west line and considered positive. Regarding ‘a’, it is said by Bhāskara व्यस्तगोला which means that when δ is north and the Sun is said to be in northern hemisphere, a is said to belong to the southern hemisphere. Also when the Sun is on the north of the prime-vertical and Śankubhuja is considered north, the Chāyābhuja being south of the East-west line is considered south. With these conventions of directions (we say of directions, and not signs because the Hindu astronomers do not speak of signs but only of directions) it is stipulated in Hindu astronomy that quantities of like directions are to be added, otherwise their difference is to be taken ‘तुल्यदिशोर्योगः, भिन्नदिशोः अन्तरम्’. This convention stipul- ating addition or difference is technically called ‘संस्कार, Samskāra’. That is why it is said simply “पलच्छायया सौम्यया संस्कृता” ie. ‘Samskāra (on the aforesaid lines) is to be effected between a and s to get bhuja b’. Here it may be reiterated that the word ‘अन्तरम्’ ie. ‘difference’ is used in its restricted sense namely that the positive difference alone is to be taken. Thus the ‘antaram’ of 8 and 5 is 3 as well as that of 5 and 8 is also 3. Then it might be asked how to decide the direction of the bhuja, if we were to take s as equal to a ~ b and not a-b or b-a. The answer is that between a and s whose directions are known as per the aforesaid convention, equating their difference ie. a ~ s to b, we have to take b as having that direction which is indicated by that quantity either a or s which has a larger numerical value. Thus while on modern lines we take a = b + s to hold universally with the convention of signs which we have agreed to on modern lines namely that a is +ve if δ is north and b is positive if the Hindu azimuth is north of the East point and s is always +ve, we take on the Hindu lines a ± s = b with the conventions stipulated with respect