If you are using the code correctly, the graphic should resize to the users monitor. It then remains as to how much of the frame you can fill up.
If you use the (1mb) max size on PB, you get the frame filled to the size of the screen and the cursor turns to a (+)- sign so the viewer can magnify if they wish.
If you use a smaller then 1 mb size, it still creates the "monitor sized" frame, but you dont have the data to fill it, so they get white space around the outside of the graphic, thereby wasting screen real estate.
