understanding currency exchange...

[Joshua Chambers]

Okay, so I still can't get the currency exchange dialog to work in a way
that makes sense to me.  I've just re-read the tutorial it all, and I
must say it lacks screenshots of what the transactions look like after
the currency exchange dialog... let me give a simple example and please
point out what I'm doing wrong.

I have two asset accounts...

-Assets:Exchanges:Benjamin (USD)
(a friend who I made a small loan to)

and...

-Assets:Holdings:Cash:Euros (EUR)
(my holdings in Euro cash, of course I have one for dollars too, but it
isn't relevant here)

Now, I understand that in double entry accounting, all the accounts need
to be balanced against each other.  I've been using gnucash for years
now to keep track of my personal accounts and some non-profits and I
really like it and get it!

However, with different currencies, two different "numbers" are actually
of equal value... so in the case of the small loan I made to my friend,
he paid me back when I visited him in Austria, paid me back in Euros...
and the rough exchange rate we made at the time (close to the current
one), is he owed $500 and paid EUR450 back.  These were equal (and still
roughly are).  That is an exchange rate of 0.9.

So I go to enter this transaction into gnucash (newest version 2.6.9)...
no matter what exchange rate I enter in the exchange rate dialog, once I
come back to the transaction I still cannot have those two be the only
parts of the transaction, I am still left over with "50" to deal with,
but there shouldn't BE 50 anythings left over, because 500USD = 450EUR @ .9!

Account                                    Debit           Credit
Assets:Exchanges:Benjamin    USD500
Assets:Holdings:Cash:Euros                         EUR450
(this is where I'm asked to balance it with another account, and if I
leave it blank, it becomes "Imbalance-USD")

So please tell me I'm missing something.  I would expect that there
needs to be some indication in the transaction what the exchange rate is
that allows them to balance up.  I would really appreciate your insight
on this confusion of mine.

Yours,
Joshua