How to account interest rate

[Mike Leone]

Robin Chattopadhyay had this to say:
> I think even if there were a BalanceAsOfDate() function, one would be easily
> frustrated using it to calculate the interest earned on a bank account. Most
> banks (in the U.S., anyway) accrue interest daily and compound monthly. 

And change every few months lately, usually downward. In 12 months, my 
ING Direct account went from 2.0% to 1.3%. An average of -0.1% every 
couple months or so. And so the SX transaction would also need to be 
changed. And usually you find out that the rate has been lowered only 
when the next scheduled interest payment is lower than you expect it to 
be ...

> So, in order to calculate the interest correctly, you need to know the balance
> of the account for each day of the period. The dates for your transactions
> in GnuCash would have to exactly match the transaction dates that the bank
> used to post the same transaction. For a transactional account (like
> checking or N.O.W. account), this would quickly become impractical.

Simpler just to make an entry on your own, whenever you earn the interest.