Dear Dialists, My PostScript cylinder dial program (http://www.cyberspace.org/~jh/dial/) was, it pains me to say, wrong. Sorry. I hope nobody used it to determine the time of anything more important than lunch. If you downloaded it before xmax eve please recycle it and download a new one.
On the bright side, I think it's fixed now. Thanks to Fer de Vries for his website with lots of detailed formulas and thanks to the rest of you for your inspiration and stimulation, especially Luke Coletti, Robert Twilliger and John Carpenter. The cylinder dial program is general, that is, it will draw a plan for differant sized cylinders, however the default values and instructions are specificly for a common soup can. I'm aiming for the widest possible target I can and trying to put sundials into the hands of anyone and everyone who has even a passing interest so I'm trying to use the most commonly available materials I can think of. The main hurdle that stands in my way is the relative unpopularity of the PostScript format. Although I happened into PostScript programming quite by accident I've come to appreciate it's incredible power. Even if PostScript is a bit daunting at first once you learn it it makes so many things easy. What's more, it's a really interesting mixture of high level structure and low level control. Adobe's PDF is, of course, the natural choice for maximizing the potential audience for a document. Adobe Acrobat Reader comes with win98 (at least mine did) and PDF has been adopted by the US government for tax forms, etc., so it really has become the standard file format for those who need exact control of how their document comes out on various systems. PDF is derived from PostScript. Actually they say it's a subset of PostScript. Turning a PostScript file into PDF includes "unrolling" loops, so a PDF version of a PostScript file can be considerably bigger. Since they are so closely related it would seem that converting to PDF would be pretty straightforward but that isn't exactly the case. Adobe has an expensive "distiller" that does the conversion and the freely downloadable ghostscript does it too but that seems to be it. I think the reasons for this are primarily economic rather that technical. Adobe has a privatly controlled defacto standard. My problem is that tripod.com, which gives me my free cgi hosting, only allows Perl cgi scripts because of the security risk introduced by shell scripts and neither ghostscript or distiller are Perl. Another problem is the fact of irritating advertisements and cookies at tripod. On the other hand, if anyone wants to fool around with perl cgi programs on the web they have it set up so you don't have to have your file permissions or shebang lines right and it will still work, which helps. But I guess I'm pretty far off topic. Happy new year. John
