Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!cam-cl!cet1
From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.lang.postscript
Subject: Re: ruler.ps - an inch/point ruler of your very own
Message-ID: <1728@gannet.cl.cam.ac.uk>
Date: 16 Jan 90 00:53:16 GMT
References: <21772@uflorida.cis.ufl.EDU> <1990Jan14.180821.18711@trigraph.uucp> <17663@rpp386.cactus.org>
Sender: news@cl.cam.ac.uk
Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
Organization: U of Cambridge Comp Lab, UK
Lines: 19

In article <17663@rpp386.cactus.org> woody@rpp386.cactus.org (Woodrow Baker) writes:
>
>in reference to my prior posting on this topic, it should be remembered
>that a multiply by 72 is a cheap operation  ((n<<3)+(n<<6)) which is likely
>the reason that 72 was picked for points.  ...

This has to be rubbish. The numbers the interpreter has to multiply by a lot  
are the contents of the default transformation matrix; e.g. 4.16667 for a
300 dpi printer. I very much doubt if the choice was made on the basis of
such any such bit-grubbing; more likely it was `keep it simple for the users'.
Anyone from Adobe care to say?

One shouldn't forget, in this context (1) the inter- and intra-printer  
reproducability of the bit density (2) paper shrinkage. Such differences
are liable to wipe out the difference between 72 ppi and 72.27 ppi.

Chris Thompson
JANET:    cet1@uk.ac.cam.phx
Internet: cet1%phx.cam.ac.uk@nsfnet-relay.ac.uk