utility relationship for calendar?

[hal9000]

I have a table called Calendar containing a record for each period. The fields are:

PeriodID Text

EndingDate Date

gCurrentPeriodID Text / Global

I want to be able to access gCurrentPeriodID and corresponding EndingDate from anywhere in my solution.

I think I need to create a relationship that allows me to look up EndingDate where PeriodID = gCurrentPeriodID. I tried that, but could not get it to work.

What's the best way to access gCurrentPeriodID and corresponding EndingDate from anywhere in my solution?