I followed your instructions to set a global variable on a calculated field:
Set(MyCalFigure,1Sum(GalleryHours.AllItems, HOURS)) in a button on screen 1
l added a label and put the Variable on the Text property: MyCalFigure1.
I did the same for 2 other screens which are records from the Main gallery MyCalFigure2 and MyCalFigure3 but nothing is showing in the global variables collection. Each variable shows "No Value" in the variables collection info.
I would like to add the total of these 3 variables together on the main gallery screen MyCalFigure1+MyCalFigure2+MyCalFigure3 but this doesn't work.
It may be worth noting that the Hours used in the calculation are in 'GalleryHours' not the Main Gallery - does this matter?