#### Checking the Expression for Correctness

When your cursor leaves the field where you added the expression, PC-DMIS attempts to check the expression for correctness. If there is a problem with the expression, an error message indicating an invalid number may appear, or the expression text may turn red. Also, expressions that refer to non-existent objects will show up in red text.

Since the test of expression correctness occurs at the time you leave a field, a field that turned red due to a reference of a nonexistent object, (ex. CIRCLE1.X), will remain red even if the new object, (ex. CIRCLE1), is added. The field remains red until the expression is re-tested for correctness.

To re-test the expression for correctness:

1. Move your cursor to the field of the expression.

2. Press the F2 key. The Expression Builder dialog box opens again. Any changes to your expression appear in the edit box.

3. Press the ENTER key to close the dialog box.