Section 3--106. Sum Certain.

(1) The sum payable is a sum certain even though it is to be paid

(a) with a stated rate of interest or by stated installments; or

(b) with stated different rates of interest before and after

default or a specified date; or

(c) with a stated discount or addition if paid before or after

the date fixed for payment; or

(d) with exchange or less exchange, whether at a fixed rate or at

the current rate; or

(e) with costs of collection or an attorney's fee or both upon

default.

(2) For the purposes of subsection one of this section "a stated rate
of interest" shall also include a rate of interest that cannot be
calculated by looking only to the instrument but which is readily
ascertainable by a reference in the instrument to a published statute,
regulation, rule of court, generally accepted commercial or financial
index, compendium of interest rates, or announced rate of a named
financial institution.

(3) Nothing in this section shall validate any term which is otherwise
illegal.