reg --display-total='amount * 10' books
<<<
2008/01/01 January
    Expenses:Books          $10.00
    Assets:Cash

2008/01/01 End of January
    Expenses:Books          $10.00
    Assets:Cash

2008/01/01 January
    Expenses:Books          $10.00
    Assets:Cash

2008/01/01 End of January
    Expenses:Books          $10.00
    Assets:Cash

2008/01/01 January
    Expenses:Books          $10.00
    Assets:Cash

2008/01/01 End of January
    Expenses:Books          $10.00
    Assets:Cash

2008/02/01 February
    Expenses:Books          $20.00
    Assets:Cash

2008/02/01 End of February
    Expenses:Books          $20.00
    Assets:Cash

2008/02/01 February
    Expenses:Books          $20.00
    Assets:Cash

2008/02/01 End of February
    Expenses:Books          $20.00
    Assets:Cash

2008/02/01 February
    Expenses:Books          $20.00
    Assets:Cash

2008/02/01 End of February
    Expenses:Books          $20.00
    Assets:Cash

>>>1
08-Jan-01 January               Expenses:Books               $10.00      $100.00
08-Jan-01 End of January        Expenses:Books               $10.00      $100.00
08-Jan-01 January               Expenses:Books               $10.00      $100.00
08-Jan-01 End of January        Expenses:Books               $10.00      $100.00
08-Jan-01 January               Expenses:Books               $10.00      $100.00
08-Jan-01 End of January        Expenses:Books               $10.00      $100.00
08-Feb-01 February              Expenses:Books               $20.00      $200.00
08-Feb-01 End of February       Expenses:Books               $20.00      $200.00
08-Feb-01 February              Expenses:Books               $20.00      $200.00
08-Feb-01 End of February       Expenses:Books               $20.00      $200.00
08-Feb-01 February              Expenses:Books               $20.00      $200.00
08-Feb-01 End of February       Expenses:Books               $20.00      $200.00
>>>2
=== 0