You can either fix the error by changing your formulae so that you do not
have a circular reference, typically by inserting an extra step.
for example calculate funds_before_interest, the interest on the
funds_before_interest and then funds_after_interest
Or if you really have a circular system you can use Iteration
(Tools-->Options-->Calculation-->Iteration), but be careful because this
tends to make it more difficult to find errors.
