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From: rudenko@cs.umass.edu
Newsgroups: comp.lang.postscript
Subject: Re: 72.27! (was Re: ruler.ps - an inch/point ruler of your very own)
Message-ID: <8696@dime.cs.umass.edu>
Date: 17 Jan 90 23:54:32 GMT
Sender: root@dime.cs.umass.edu
Organization: COINS, UMass, Amherst
Lines: 49


According to the Red Book, section 4.4, page 61,
	"The unit size, 1/72 of an inch, is very close to the size of a
	printer's point (1/72.27 inch), which is a standard measuring
	unit used in the printing industry."

I tried drawing a vertical line 10 inches long on a (300 dpi) DEC LN03R via:
	0 setlinewidth   % thinnest possible line
	newpath
	100 10 moveto
	0 720 rlineto stroke    % 10 inches * 72 pts per inch

	% mark end points
	95 10 moveto
	10 0 rlineto stroke
	95 730 moveto
	10 0 rlineto stroke
	showpage

I measured the length of the resultant line with a steel rule and got a
length of about 9 31/32 inches.  Wondering if the PostScript point was
really 1/72.27 inch, I tried:

	0 setlinewidth   % thinnest possible line
	newpath
	100 10 moveto
	0 722.7 rlineto stroke   % 10 inches * 72.27 points per inch

	% mark end points
	95 10 moveto
	10 0 rlineto stroke
	95 732.7 moveto
	10 0 rlineto stroke
	showpage

The resultant line turned out to be just a hair over 10 inches long!
Sending the file to the printer a second time produced lines of 9 61/64 and
a hair short of 10 inches, respectively.  Sending the file to the printer a
third time yielded lines a hair short of 9 31/32 and as close to 10 inches as
I could measure, respectively.  All measurements were double checked with
a second ruler.

This experiment seems to indicate that the size of PostScript point is
apparently equal to the printer's point, 1/72.27 inch, and not 1/72 inch as
claimed by Adobe!?

-- Michael Rudenko
rudenko%coins@cs.umass.edu
rudenko@umass.bitnet