Re: First experience with a slide rule Message #2 Posted by Garth Wilson on 12 Aug 2013, 1:49 p.m., in response to message #1 by aurelio
There shouldn't be any paralax, as the hairline on the rear surface of the glass gets pressed down against the rule. If it's well made and not out of adjustment, you can usually (depending on the function) get at least three digits of accuracy, sometimes more. Although it may be hard to believe for someone who's used to anywhere from 10 to 20 digits on a calculator or computer, 3 is actually plenty for a large portion of engineering work.
When trying to show a beginner, something I always see is their frustration with trying to get an exact adjustment on either the slide or the cursor. There's a way to hold it to get the effect of a vernier as your roll your fingers. It occurs to me now there's probably a way I could illustrate that on my slide-rule page, http://wilsonminesco.com/SlideRules/SlideRules.html
There were the cylindrical rules (see http://www.hpmuseum.org/srcyl.htm) which had scales 50 times as long, wrapped around a cyclinder to make the size manageable. I've never seen one in person, let alone used one, but it looks like you would normally get 4-5 significant digits; but it did not have all the scales that a normal slide rule had.
Vision is of course necessary, but corrective lenses should take care of that for most people. I'm nearsighted, and even at age 53, it's only a small exaggeration to say I can see germs at 6" (15cm) without glasses.
In the 1970's after all my classmates had gone to calculators, I kept using a slide rule for a few more years because I could see its value in helping understand number relations. Even today, when discussing something with the other engineer I work with, I do the decibel conversions (requiring the common logarithm) instantly in my head, and he says, "How do you do that so fast?" I replied, "You're just slightly too young to have used a slide rule, huh?!" I went to a calculator when I needed something programmable, a requirement the slide rule could never meet. First I got a TI-58c, then a TI-59, then the HP-41cx.
Edited: 12 Aug 2013, 1:51 p.m.
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