Just a quick example may look like this:
5/1/2016. Net Liquidation Value = $100,000
5/2/2016. Buy 300 x SPY at $205.
5/28/2016. Sell 300 x SPY at $209.
May Profit/Loss = $1,200
May Return = + $1,200/$100,000 = +1.2%
6/1/2016. Net Liquidation Value = $101,200
6/17/2016. Buy 300 x SPY at $207...