printRectangle

[Richmond]

Um . . .

connected up my printer and turned it on (yes, oddly enough I have looked
a "right banana" when I haven't done that in the past) and typed this into
the message box:

put printRectangle   and got 0,0,612,795

put printPaperRectangle   gave me the same result

PRESUMABLY that means that my printable area is 612 wide by 795 high;

whether that is US letter or A$ or some rococo size only available in 
Burkino Faso
has to be set by printPaperSize

tried this  set printPaperSize to "B3"   and got nowhere (!!!!) so, I 
assume, one has
to "know" one's paper sizes in terms of pixels . . . . Oink, Oink, Oink.

Now what IS NOT clear to me is whether, when I muck about with the 
printMargins,
the printRectangle will change:

Let's have a go:

set the printMargins to 200,200,200,200

and

put printRectangle gives me  0,0,612,792

No joy there!

SO, my question is . . . how does one find out what the printable area is
WITHOUT having to muck about mathematically subtracting printMargins 
from printRectangle?