2014/06/01 Deposit some cash
  Equity:OpeningBalances
  Assets:Investing:Cash        $20000

2014/06/02 Buy one lot
  Assets:Investing:Stocks       10 MSFT @ $500
  Assets:Investing:Cash

2014/06/03 Sell the lot
  Assets:Investing:Stocks      -10 MSFT {$500} @ $510
  Assets:Investing:Cash

P MSFT $520

2014/07/02 Buy one lot
  Assets:Investing:Stocks       5 MSFT @ $530
  Assets:Investing:Cash

2014/07/02 Buy one lot
  Assets:Investing:Stocks       5 MSFT @ $540
  Assets:Investing:Cash

P MSFT $550