In the Define Function dialog, you will get an error message if there is something wrong with the expression that you entered. You will not be able to OK the dialog until the expression you enter is valid.
Syntax Error in Expression. You entered something that doesn't make sense, such as **, for example.
Unmatched Parentheses. The number of left and right brackets are not equal. You must have matched parentheses for the expression to be valid.
Unknown Operator. You entered something that looks like an operator but isn't, such as SIL(x) instead of SIN(x).
Out of Memory. There was insufficient memory to evaluate the expression.
Expression too long or complex. The expression exceeds 255 characters in length or it contained terms that were so deeply nested that an error occurred trying to evaluate it. The second case is very rare.
