Surya Siddhanta
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लब्धम् प्राच्याम् ऋणम् सौम्याद् विक्षेपात् पश्चिमे धनम् । दक्षिणे प्राक्कपाले स्वम् पश्चिमे तु तथा क्षमः॥
The result, when latitude is north, is subtractive in the eastern hemisphere, and additive in the western ; when latitude is soitth, on the other hand, it is additive in the eastern hemisphere, and likewise subtractive in the western.
english translation
Chapter 7
Verse 8
Verse 10