IIf formula in microsoft project custom field

John-project 

John - So for this project file, this is not a typical project phased type model. What i am being asked to build is a single-file schedule with small (8-12 lines) individual repair efforts for various locations; each with its own PoP end dates set a deadlines. Each of these repairs would roll up to its own summary, so at the summary level, it would provide easy visibility into the target deadline for each repair vs. current status of each. For tasks that are 100% complete, the total slack field at the summary level will not ignore 100% completed tasks, but i have now found a formula that works well for this when applied to a custom duration field, so my initial issue has been resolved.