Acount Derivation Rule

Hi,

We are implementing release 12.1.2 for Oracle Projects and have a requirement to create the cost center based upon the Account segment generated in AutoAccounting.  We've determined that SLA is the best means to address this - the obivous question is of course how.  What we would like to be able to do is set the cost center segment to a value if the Account segment is less than a value.  We've attempted to write an Account Derivation Rule to determine this but are struggling with how to get the condition to reference being less than or equal to a constant value.  Anyone had any