Re-Sizing PostScript Scales

Accuracy of printed scales

PostScript itself is will print to the precision available on a printer.

If you can print a slide rule on standard paper, you should expect to obtain accurate results with a home printer, not more than 1/2 mm deviation.

I use letter size paper settings in my PDF production, and usually try to squeeze as much space a scale. This can mean full-sized scales will be clipped on A4 paper. I can generally re-size the pages in PostScript to match the page size, but if the scales are for repairing an instrument a 100% true fit is needed. In such case, a metric size like A3 might be needed. I haven't had this happen yet, though.

Adobe Reader problems

Adobe Reader is the product commonly used to view and print PDF files.

PDF files sometimes are affected by default print settings. Those can be usually be managed by fiddling with the printer settings page.

The most common problem has to do with a default setting that scales pages 'to fit' the paper you have. If you aren't expecting it, your scales might be a bit shorter than nominal. On the other hand, this feature addresses the A4 clipping problem, and is suitable for most applications.

Genuine printer problems

• Paper stretches with relative humidity. The effect is not normally noticeable on the page sizes that home printers use. It might affect the quality of some scale configurations, helical scales in particular.
• When scales are sufficiently long, they would need to be printed at a printshop or stationery store. Experience with very long scale rules suggests that sometimes there's a higher deviation with long scales. This could be related to paper stretching effects, or just the fact that much more paper needs to be fed through a machine, allowing for minor inaccuracies to become visible.
• Bob Wolfson had a lot of trouble getting an accurate 18 inch x 20 bar Thacher scale printed. I believe Bob’s issue to have been mechanical – most commercial printers aren’t designed for the degree of large scale accuracy needed for such big prints. Bob had to take the scales around to multiple print firms before he found a printer that had adequate gear.

Custom sizes

PostScript has a command that permits size scaling; you can shrink or expand any thing on a page. All my Postscript files contain this command, set to "1 x magnification". I change the default setting to adjust the size of the output to fit the material I have.

Originally, I had thought this would be perfect technique for other makers, and planned to distribute my PostScript files and fonts. Unhappily I learned very early that native PostScript is not something most people can work with, particularly when using custom fonts, and so I switched to distributing them as PDF files.

The scales I produce are designed print at the nominal size of the slide rule. The "nominal size" I use may be suspect, given that I'm often taking my guidance from what I can read on various websites with photos of the original model, rather than original sources.

When making replica slide rules at home, most people are using whatever they have handy, and particularly for cylindrical rules this means whatever sized tubes they have on hand. My Postscript scales need to be stretched or shrunk to be fitted to the media available to the builder.

The fact that the underlying media (usually cardboard cylinders) is a bit hard to measure accurately with tools available to the average builder; this means scales may have to be adjusted a few times to get an exact fit.

Today, I resize scales for people on request, as the majority of people who contact me are using custom sized materials. There are products like Adobe Acrobat that offer this re-sizing capability, plus some online sites that might work as well. I've not tried them, so don't know how effective they are.