MS Project task-level calculated custom field displaying incorrect value

Question

I have a custom field defined on a task level that is calculated using the value of another task-level custom field.

The value of the calculated field, "Completed" is either 1 or 0, based on the value of the other field "Completed Date." If Completed Date has a value, Completed = 1, else Completed = 0. Completed Date is a Date type field.

I am currently having a problem where in a handful of cases, Completed is 1 when Completed Date has no value.

The formula for Completed is

IIf(IsDate([Completed Date]) = True, 1, 0)

99% of the values calculate correctly, but the 1% is causing problems. The only way to correct the value of Completed is to put a value in Completed Date and then remove the value from Completed Date.

Has anyone else experienced Project calculated fields calculating incorrectly like this? Are there any fixes?

Answer 1

The solution that worked for me, provided by Ismet Kocaman over at the MSDN forums, was:

Do not use IsDate for NA check. Instead, use iif( [Completed Date] = ProjDateValue("NA"), 0, 1 )