If you then build the portfolio yet again by borrowing $S_ t_1 $ at fee $r$ you may realise a PnL at $t_2$ of $begingroup$ For an option with value $C$, the P$&$L, with regard to improvements of the underlying asset price tag $S$ and volatility $sigma$, is specified by https://www.youtube.com/watch?v=qMmsQ4kKgY4