reg -V gas
<<<
2009/01/01 Payee
    Expenses:Gas                100 GAL {=$2}
    Liabilities:MasterCard        $-200

2009/01/01 Payee
    Expenses:Gas                100 FOO {$2}
    Liabilities:MasterCard        $-200

P 2009/03/01 12:00:00 GAL $3
P 2009/03/01 12:00:00 FOO $3
>>>1
09-Jan-01 Payee                 Expenses:Gas                   $200         $200
09-Jan-01 Payee                 Expenses:Gas                   $200         $400
09-Mar-02 Commodities revalued  <Revalued>                     $100         $500
>>>2
=== 0