Calibrating pbm2ppa for Your Printer

  Upon being able to print successfully, you can calibrate your printer with
the 'pbmtpg' program (PBM test-pattern generator).  Calibration basically
consists of centering the output on the page in order to allow for a
reasonable maximum printing area.  [Note: if attempting to print only causes
all three lights to blink, try widening the margins to something ridiculous
during this procedure (like 600)]
  The 'pbmtpg' program generates a full-page (8.5"x11") test pattern in
pbmraw (P4) format on stdout.  The output may be fed directly into pbm2ppa
in order to print a calibration pattern on your printer with commands such as:
Assuming you printer is on /dev/lp0

    pbmtpg | pbm2ppa > /dev/lp0
      ( as root )
(Note: /dev/lp0 is the default device for the primary parallel port on systems
with 2.2.x or later Linux kernels; it is /dev/lp1 on  systems with
older Linux 2.0.x kernels)

For other papersizes, the command must specify a valid size, for both
pbmtpg and pbm2ppa:

    pbmtpg -a4 | pbm2ppa -s a4 > /dev/lp0
    pbmtpg -legal | pbm2ppa -s legal > /dev/lp0
    pbmtpg -letter | pbm2ppa -s letter > /dev/lp0

For A4, US Legal of US Letter (default).

      - or -

    pbmtpg | pbm2ppa | lpr -l
      ( if your printer filter recognizes the '-l' (direct output) parameter )

  The numerical values marking grid intersections are pixel coordinates.
Unfortunately, these coordinates are probably cut off before the edge of the
paper.  You'll have to use a ruler to estimate the pixel coordinate of the 
left and top edges of the actual sheet of paper (should be within +/- 300, may
be negative, there are 600 pixels per inch).
  Add these coordinates to the X and Y offsets by either: (1) editing the
defaults.h file and recompiling, (2) modifying the default values in
/etc/pbm2ppa.conf, if you've set this up, or (3) using the '-x' and '-y'
command-line parameters.
  When properly calibrated, the center mark should be in the center of the
paper.  Also, the margins should be able to be as small as 1/4 inch without
causing the printer to choke with 'blinking lights syndrome'.

[TODO: Add shearing adjustments to pbm2ppa and explain here]