If I have a "Current Date" Calculation field stored as a Global, it only gets updated when the host file is opened. And if the host file sits on a server, it may sit there for literally months showing the same date that it had when the file was last opened.
OTOH, if I set it to Unstored, there's a performance hit, because FileMaker has to run the calculation on that field — and every field dependent on it, such as "Age" or "Year in School" or "Time to Deadline" — every time I need it for a display or calculation.
So it's a tradeoff between accuracy and speed, when of course I want to have it all. (Who doesn't?)
It seems that the ideal solution would be a script that would run at a minute past midnight every day to look up the current date for a Date-type (not Calculation-type) Global field. But I'm not aware of any FileMaker Pro script step that would do this. Is there such a procedure?