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Slide Rule


Sedalia Dave

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I remember my dad showing me his from pharmacy school in the 50's. Had this little slide (hence the name) that floated around in the middle, it had two scales, at least four scales two inner two outer on the outside part, and a little gizmo on the outside that slid with a straight line etched on it. He tried to show me how to use it and 'bout gave me a migraine. :lol: I don't remember how old I was, jr or sr high school I guess. Had to be a smart cookie to use one of those. Must have been Einstein that invented it! That was somewhere about the the time the TI-30 calculator came out. I was like God bless Texas Instruments! I guess they worked. We invented atomic bombs and went to the moon by men using those.

JHC

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I have a slide rule in my tool box. I had 2. I showed my grandson how to do basic multiplication on one. He was intrigued so I gave him one of them.

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My slide rule disappeared years ago and I since have forgotten all but the very basics of how to use one!!

 

Thanks for posting, Dave!

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I bought a slide rule to use for high school senior year Physics class. I learned to use it for multiplication/division and for Trig functions. When I joined the Navy and went to nuclear power school I learned to use most of the scales. The Navy issued slide rules but I used my own. I have it still. It is the one at the top of the picture. The one below is one my father gave a neighbor kid back in about 1965, that guy returned it to me in 2002. the others are some I picked up at random places. About all I remember is multiplication and division. At the Navy nuke school, we had to use the slide rule on tests even though electronic calculators had come way down in price and size. 

sliderule.JPG

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Same story as Dustin Checotah - the Navy wouldn't let us use electronic calculators in school. I still have my old Pickett in my desk, but little clue how to use it anymore.

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I thought the slide rule was: wait til the kid at the bottom got out of the way before you go.

 

I musta hung out with a different crew than you guys

 

 

 

 

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I did University Interscholastic League slide-rule competitions three years in high school.  My father taught me how to use one in the 50's. He was an air traffic controller and they used them to compute several flight solutions in radar approach control.  He enlisted in the Air Force in 1950 and went into radio and radar.  I still use one of the several I have for lots of things.  Hmm two under this keyboard.,

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I used one in college for my structural engineering calc's. I could do the math but lost the decimal placement more often than not. The library had table mounted electronic calculators you could use for $.25/hour. I went to   the library to get my math correct.

 

1975 a Texas Instrument calculator was $400. Within 3 years you could get a great calculator for $50.

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My grandfather was  CA registered EE & ME.  He gave me a new K&E slide rule for high school graduation & acceptance to UCB College of Engineering (his Alma Mater).  I still have it and haven't used it since I bought a TI math function calculator in 1977 from a former coworker who then worked for TI.  The employee cost was dirt cheap.

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Back in the mid '60's I had a Summer job working with Disturbed kids at a camp. Another councilor working there was an engineering student and had brought his slipstick and some course books.  One of the kids, we'll call him Robert, was a math savant.  He could work problems out in his head as quickly as could be done with the slide rule.  He used to give himself verbal instructions for simple things "Time to get up, Robert." Never forgotten him. Amazing.

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A story about slide rule accuracy.

 

I took Heat Transfer in college during the slide rule era. My ex took it about 8 years later when calculators were common. She had the same (but newer) textbook that I used. I still had all of my workbooks and problem solutions that she would use to check her work. Note that she did know how to use a slide rule. 

 

The solutions from my text book were to slide rule accuracy and she would work to that level. The solutions in her text book were to calculator accuracy and were, at times, up to 25% different so she got dinged in grading with the slide rule accuracy answers!

 

Now, after I graduated, I had a long career in heat transfer in the chemical / petroleum industries. I would call heat transfer in those industries a black art as all of the properties of the fluids were of an approximate value as the mixtures were never consistent as were the flows and temperatures. 

 

Add to this that all of the formulas for heat transfer were based upon pure component fluids and all anything else was extrapolated based upon the component mixture. So experimental data almost looked like a shotgun target of data points and the formulas would be adjusted to an "average on the safe side" to fit the data. So for some cases, boiling mainly, the formula could be 25% off from some data points.

 

Now add to that the 25% difference in solutions that were obtained by taking the slide rule derived formula and applying 16+ digit "accuracy" of calculators and computers and you could possibly be adding a significant error to a solution.

 

This is where the "black art" came in, you had to develop a sense of what the approximate value should be and not completely trust what the computer analysis came up with.

 

We had numerous situations where an office (usually foreign) with inexperienced engineers would just run with the computer analysis and incorrectly design the equipment resulting in enormous cost increases as well as malfunctioning equipment.

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19 hours ago, irish ike, SASS #43615 said:

1975 a Texas Instrument calculator was $400. Within 3 years you could get a great calculator for $50.

 

In my high school chem class, 1972,  the first week was devoted to learning to use a slide rule. One guy got a pocket calculator that Christmas.  MAN!  Four functions!  We all oohed and awed over it.  Two years later we all had them.  

 

13 hours ago, Injun Ryder, SASS #36201L said:

The solutions from my text book were to slide rule accuracy and she would work to that level. The solutions in her text book were to calculator accuracy and were, at times, up to 25% different so she got dinged in grading with the slide rule accuracy answers!

 

In junior college, O-chem class, I got marked wrong on a test answer.  I reworked it and got the same answer.  I asked the instructor how my answer was wrong.  He pointed out that I ran it out to something like 5 or 6 decimals.  So?  He asked me how many significant figures on various things,  "Two, maybe three" I said.  He pointed out that by going beyond that I was possibly, likely, introducing error no matter what the calculator showed.  

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Speaking of early calculators. The HP80 came out in my Sr year. It did not have any built in functions, everything was read from a magnetic card. One of the junior engineers bought one and our electrical engineering professor was so concerned that he would program some test problems on some cards and use them during the tests that he made the student put a piece of tape over the card reader during tests thus rendering an $800 calculator almost useless!

 

I bought a Texas Instruments SR-10 in my Jr year but it was limited to four functions, squares, square roots and exponents. I carried a small trig book in the case and my slide rule so that I could be fully functional.

 

When I started to save for it in the spring it was $175 but fortunately for me it came down to $125 by the start of the fall semester. That was still over two weeks pay for me at the time!

 

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On 3/18/2023 at 10:22 PM, Dustin Checotah said:

I bought a slide rule to use for high school senior year Physics class. I learned to use it for multiplication/division and for Trig functions. When I joined the Navy and went to nuclear power school I learned to use most of the scales. The Navy issued slide rules but I used my own. I have it still. It is the one at the top of the picture. The one below is one my father gave a neighbor kid back in about 1965, that guy returned it to me in 2002. the others are some I picked up at random places. About all I remember is multiplication and division. At the Navy nuke school, we had to use the slide rule on tests even though electronic calculators had come way down in price and size. 

sliderule.JPG

Cube root is very easy.  Just direct read the D and K scales.  

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My TI-36 Solar sits on my desk, same as it has done for the last 34 years.
Runs great, is 100% reliable, and I know how to use it.
Doesn't get any better than that...

 

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