AutoShape Location

I have a large worksheet broken into pages/screen. Each screen has a button
that creates a call out. The code I have (for one location) is;

ActiveSheet.Shapes.AddShape(msoShapeLineCallout2, 750#, 400#, 72#, 48#). _
Select

This is an absolute reference (750#, 400#) to one page/screen. I do not
want to write code for each button. I need a macro that will call up a call
out and locate it in the center of the page/screen I am viewing.

Thanks a lot for any help.