Surya Siddhanta
पातकालः स्फुटो मध्यः सो +अपि स्थित्यर्धवर्जितः। तस्य सम्भवकालः स्यात् तत् सम्युक्तो +अन्त्यसाम्ज्ञितः॥
The corrected (sphuta) time of the aspect (pdta) is the middle : if that be diminished by the half-duration, the result is the time of the commencement ; if increased by the same, it is the time of the end.
english translation