Ledger is an accounting tool with the moxie to exist.  It provides no
bells or whistles, and returns the user to the days before user
interfaces were even a twinkling in their father's CRT.

What it does offer is a double-entry accounting ledger with all the
flexibility and muscle of its modern day cousins, without any of the
fat.  Think of it as the Bran Muffin of accounting tools.

To use it, you need to start keeping a ledger.  This is the basis of
all accounting, and if you haven't started yet, now is the time to
learn.  The little booklet that comes with your checkbook is a ledger,
so we'll describe double-entry accounting in terms of that.

A checkbook ledger records debits (subtractions, or withdrawals) and
credits (additions, or deposits) with reference to a single account:
the checking account.  Where the money comes from, and where it goes
to, are described in the payee field, where you write the person or
company's name.  The ultimate aim of keeping a checkbook ledger is to
know how much money is available to spend.  That's really the aim of
all ledgers.

What computers add is the ability to walk through these postings,
and tell you things about your spending habits; to let you devise
budgets and get control over your spending; to squirrel away money
into virtual savings account without having to physically move money
around; etc.  As you keep your ledger, you are recording information
about your life and habits, and sometimes that information can start
telling you things you aren't aware of.  Such is the aim of all good
accounting tools.

The next step up from a checkbook ledger, is a ledger that keeps track
of all your accounts, not just checking.  In such a ledger, you record
not only who gets paid---in the case of a debit---but where the money
came from.  In a checkbook ledger, its assumed that all the money
comes from your checking account.  But in a general ledger, you write
posting two-lines: the source account and target account.
@emph{There must always be a debit from at least one account for every
credit made to another account}.  This is what is meant by
``double-entry'' accounting: the ledger must always balance to zero,
with an equal number of debits and credits.

For example, let's say you have a checking account and a brokerage
account, and you can write checks from both of them.  Rather than keep
two checkbooks, you decide to use one ledger for both.  In this
general ledger you need to record a payment to Pacific Bell for your
monthly phone bill.  The cost is $23.00, let's say, and you want to
pay it from your checking account.  In the general ledger you need to
say where the money came from, in addition to where it's going to.
The transaction might look like this:

@smallexample
9/29  BAL  Pacific Bell              $-200.00   $-200.00
           Equity:Opening Balances    $200.00
9/29  BAL  Checking                   $100.00    $100.00
           Equity:Opening Balances   $-100.00
9/29  100  Pacific Bell                $23.00    $223.00
           Checking                   $-23.00     $77.00
@end smallexample

The first line shows a payment to Pacific Bell for $23.00.  Because
there is no ``balance'' in a general ledger---it's always zero---we
write in the total balance of all payments to ``Pacific Bell'', which
now is $223.00 (previously the balance was $200.00).  This is done by
looking at the last transaction for ``Pacific Bell'' in the ledger, adding
$23.00 to that amount, and writing the total in the balance column.
And the money came from ``Checking''---a withdrawal of $23.00---which
leaves the ending balance in ``Checking'' at $77.00.  This is a very
manual procedure; but that's where computers come in...

The posting must balance to $0: $23 went to Pacific Bell, $23 came
from Checking.  There is nothing left over to be accounted for, since
the money has simply moved from one account to another.  This is the
basis of double-entry accounting: that money never pops in or out of
existence; it is always a posting from one account to another.

Keeping a general ledger is the same as keeping two separate ledgers:
One for Pacific Bell and one for Checking.  In that case, each time a
payment is written into one, you write a corresponding withdrawal into
the other.  This makes it easier to write in a ``running balance'',
since you don't have to look back at the last time the account was
referenced---but it also means having a lot of ledger books, if you
deal with multiple accounts.

Enter the beauty of computerized accounting.  The purpose of the
Ledger program is to make general ledger accounting simple, by keeping
track of the balances for you.  Your only job is to enter the
postings.  If a posting does not balance, Ledger displays an
error and indicates the incorrect posting.@footnote{In some
special cases, it automatically balances this transaction for you.}

In summary, there are two aspects of Ledger use: updating the ledger
data file, and using the Ledger tool to view the summarized result of
your transactions.

And just for the sake of example---as a starting point for those who
want to dive in head-first---here are the ledger transactions from above,
formatting as the ledger program wishes to see them:

@smallexample
2004/09/29 Pacific Bell
     Payable:Pacific Bell            $-200.00
     Equity:Opening Balances

2004/09/29 Checking
     Accounts:Checking                $100.00
     Equity:Opening Balances

2004/09/29 Pacific Bell
     Payable:Pacific Bell              $23.00
     Accounts:Checking
@end smallexample

The account balances and registers in this file, if saved as
@file{ledger.dat}, could be reported using:

@example
$ ledger -f ledger.dat balance
$ ledger -f ledger.dat register checking
$ ledger -f ledger.dat register bell
@end example