When you close the message, Excel displays either a zero or the last calculated value in the cell. And now you're probably saying, "Hang on, a last calculated value?" Yes. In some cases, a formula can run successfully before it tries to calculate itself. For example, a formula that uses the IF function may work until a user enters an argument (a piece of data the formula needs to run properly) that causes the formula to calculate itself. When that happens, Excel retains the value from the last successful calculation.