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<html>
<body>
<H1> Printer calibration </H1>
<p>
The printer calibration dialog was broken for long. In fact it was broken for
longer than pcb-rnd even existed: the version of gEDA/PCB it was forked from
already had a partly defunct calibration. (The bug is that after the calibration
the print dialog does not remember any of the calibrated values).
<p>
The whole idea of printer calibration embedded in pcb-rnd is probably not that
good. The lpr plugin is hard-wired to the ps export. The ps file format does
have units, so the only reason anyone would need a calibration is working around
printer bugs or paper shrink problems. But those problems are not related to
pcb-rnd, thus the calibration should probably be done only once, independently
of the software used.
<p>
Thus the calibration dialog box and code got removed from pcb-rnd. A new,
optional config subtree is added for export_lpr where the user can save
calibration values so that the lpr exporter remembers them. These
preconfigured calibration values are used upon any print from pcb-rnd, if
command line arguments or GUI export dialogs don't override them.
<p>
The recommended manual process for a printer calibration is:
<ul>
<li> 1. draw a rectangle in pcb-rnd that is large enough for your printer and
paper size; preferably use round sizes, e.g. on an A/4 paper,
assuming portrait printing: 150*250 mm (this leaves enough margin);
use thin lines
<li> 2. print it with pcb-rnd
<li> 3. measure width and height and calculate the calibration value per x
(horizontal) and y (vertical) direction; the calibration value is:
measured_size / drawn_size; the result should be close to 1.0.
<li> 4. final check: print again, but this time enter the calculated
calibration values in the print dialog box xcalib and ycalib fields;
the resulting printout should be very close to the exact size
<li> 5. save the calibration values in user config, either using the preferences
window tree tab and looking for plugins/export_lpr or by writing
a config file with a text editor (see below)
</ul>
<p>
Hand written config file: create a file with a text editor, call it
~/.pcb-rnd/lpr_printer_calib.conf and copy the following content in it:
<pre>
li:pcb-rnd-conf-v1 {
ha:overwrite {
ha:plugins {
ha:export_lpr {
default_xcalib = 1.0
default_ycalib = 1.0
}
}
}
}
</pre>
<p>
Modify the values of default_xcalib and default_ycalib to the ones calculated
during the above calibration process.
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