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

240 Fig. 39 or in modern terms sin δ = sin ϕ cos z + cos ϕ sin z sin a as derived from the triangle PZS. Formula I is with respect to the Mahā Śaṅku ⊙ L of fig. 40; if it be reduced to the Śaṅku of the gnomon the Śaṅku-bhuja ⊙ N becomes the Chāyābhuja pr which will be equal to (H sin z H sin a / R) × (K / R) = K sin z sin a whereas, Agrā becomes (R H sin δ / H cos ϕ) × (K / R) = (K sin δ / cos ϕ) which is called Karṇāgrā and Śaṅku-tala becomes (H cos z tan ϕ × K / R) = K cos z tan ϕ = 12 tan ϕ = s, which is a constant quantity. It will be noted that Karṇāgrā differs from point to point since K differs from time to time during a day. In fact Karṇāgrā is the perpendicular dropped from the extremity of the shadow