Printing query

[David Squance]

Hello Group,
I've created a little app to print labels, and am trying to adapt it to do
envelopes.  I'm having trouble getting my head around the numbers.  I have
the rect of the fld to which the address info goes, and have the handler
print the card from the first two numbers of the fld rect to the last two.
This is a segment of the printing handler:

  if the platform is "MacOS" then answer printer
  else set the printrotated to true
  open printing with dialog
  if envchoice is "short" then
    set the printPaperSize to 261,468
    set the printmargins to 200,144,36,36
  end if
  if envchoice is "long" then
    set the printPaperSize to 297,684
    set the printmargins to 360,144,36,36
  end if
  print this card from 4,31 to 193,103
  close printing

When I print (to PDF) on my Mac (since RR crashes if I try to do a real
print), the fld is all there, but on Windows, I lose most of the field.
What's the interconnection between the various sets of numbers?  The
papersize is just 72 X the dimensions of standard (North American)
envelopes, and the margins are supposed to put the address in the right
place on the envelope.  Any enlightenment would be helpful.
Dave