Assume you bought and sold 75 Nify 7000 calls at Rs 100.
Premium turnover : (75 x 100) + (75 x 100) = Rs 15000
Notional turnover : (75 x (7000 + 100)) + (75 x (7000 + 100) )= Rs 10.65 lakhs
Exchanges declare turnover on notional basis (one sided). But for all practical purposes from calculating STT to all other taxes only the premium turnover is taken.