$ Inside the "do the job situation" you liquidate the portfolio at $t_1$ realising its PnL (let me simplify the notation a tiny bit) Depreciation = value originally on the yr (opening harmony) + purchases in the 12 months − benefit at the end of the 12 months (closing equilibrium) https://messiahoglpt.bloguerosa.com/33068692/how-much-you-need-to-expect-you-ll-pay-for-a-good-pnl