Before There Was Calculators.

Rule #1, Slide rules need no batteries!
My first really good calculator was an HP35. Reverse polish is better in my opinion..........I miss it still.

Need help! I can’t find the Equal Sign.
 
Several years ago I had taken my mother to a doctor out of town and she saw an antique shop she wanted to stop at. I went in too, and saw a strange device like I had never seen before. I think it was marked $25; if that isn't it, it wasn't much more. I didn't have a clue what that thing was and left it on the shelf. About three years ago I ran across something about Curtas somewhere and remembered seeing that one in the antique store. Still kick myself for not buying it. I just had a feeling it was worth something and talked myself out of buying it.
 
I used a circular slide rule all through college. The HP35 was introduced when I was a Senior EE student but was way too pricey. I still have the circular (somewhere). At work I'd occasionally drag it out to show to my younger colleagues, telling them it was a calculator that worked without batteries.
 
I was at an antique store in Frederick, Maryland yesterday and the guy had a very large slide rule that looked to be maybe a teaching aid and it was about 4 feet long by about 10 inches wide and everything worked. He "only" wanted $495!
 
Still have my Deitzgen engineering slide rule. And still like RPN over algebraic calculators. My slide-rule is in a glass front case with a hammer attached. And a sign saying "In case of computer failure, Break Glass". Never went to high school, picked up the EE offshore a few years later. Guess I missed all the fun of high school... ...
 
I still have my Post bamboo slide rule from when I was in college 100 years ago, complete with leather scabbard. If you ask today’s kids, “If Joe and 10 of his friends each had 4 calculators, how many calculators did Joe have?”, they’d reach for their calculator.

Tom
 
Took course in engineering curriculum - nomography - we learned how to construct the "on paper" calculators that you laid a ruler across and connected the quantities you had making the ruler cross another line with the quantity(ies) you wished. Miles per gallon calculators are an easy example. Design of pressure vessels is a complicated one. Any equation can be represented with such a chart. It was a very informative course taught by an excellent professor and it explained a whole lot about how the world works and how we approximate it to our best benefit. Now we use spreadsheets and apps to generate these types of short cuts.
 
Took course in engineering curriculum - nomography - we learned how to construct the "on paper" calculators that you laid a ruler across and connected the quantities you had making the ruler cross another line with the quantity(ies) you wished. Miles per gallon calculators are an easy example. Design of pressure vessels is a complicated one. Any equation can be represented with such a chart. It was a very informative course taught by an excellent professor and it explained a whole lot about how the world works and how we approximate it to our best benefit. Now we use spreadsheets and apps to generate these types of short cuts.
Back in the eighties, I designed a circular slide rule the would calculate the length of bar stock required to make a shoe for a horse, based on two measurements of the horse's hoof. My ex, who was a farrier, made and sold quite a few of these to other farriers.
 
Slide rules, used to love them. As a Marine Engineering student at Sydney Uni (Australia) in the early seventies, calculators were very basic and we weren't allowed to use them anyway. So it was Long hand, Log tables or a slide rule. The slide rule was by far the quickest, you just had to be careful when keeping track of the decimal point. They were in their own when it came to doing calculations involving raising a value to a power that was not a whole number as in 2, 3, 4 etc. calculations on the expansion and compression of gases in particular often involve a power of 1.3 or 1.4 etc.

I still have a couple of good old Japanese bamboo slide rules, they were the best. And a circular one as shown above, they were particularly good at trig calculations,
 
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A further more accurate slide rule was the drum slide rule used by a lot of Drawing offices. These had the logarithmic scales on the outside of a drum which could have a scale length of 500 " as opposed to the 10" normal straight linear type. Sure was a lot quicker (though not as accurate) as using log / anti-log tables ( 7 fig. tables in the D.O. !)
Happy days !
I used five place log tables a lot on college when we needed more precision than the slide rule would provide. One can appreciate the seven place tables when you realize that every additional place multiplies the number of pages of tables by ten. My five place tables in the CRC Math Handbook require 20 pages.
One can also appreciate the power of the modern calculator. The Android calculator on my phone displays 11 decimal places. To replace it with a set of log tables would require 20 million pages.
 
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