One option would be to add a Comment to the field. Right click on it in the data window and select Default Properties...>Comment.
Hope this helps!
Hi Tracy, thank you so much - i guess i was thinking that the calculation details already exist, in that when the user makes the calc, they put in a formula. so this formula exists somewhere in the guts of tableau - i'd just like to pull it out and display it.
we could indeed add a comment - this would be describing the calc twice, but anyway.
there seems to be a few people casting about for this kind of thing- so often a calc has some sort of related information.