Slide Rules & Calculators

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Zipper730

Chief Master Sergeant
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Starting in 1972 the pocket calculator came into being: Prior to that point there were basically either typewriter sized calculator machines or slide rules.

Honestly when one looks at the complexity of a slide rule: Doing long multiplication doesn't seem so hard. I'm amazed how people managed to use them. It might have made sense for trigonometry and more sophisticated functions, but it seems honestly faster to just multiple by hand.
 
Actually, the TI pocket calculators were available in 1968, when I first entered engineering school. Our freshman class had about 1,400 students, and only three could afford one of the TIs - they weren't allowed to use them on tests because of the unfair advantage. (A few years later, you got a more powerful calculator for free when you opened a checking account!)

I've still got my beautiful Post versalog, which I bought for a ridiculous $60 at the time. It wasn't hard to use, though one needed to keep track of the decimal points or risk some very strange answers on those physics tests. Had some computer geeks by the house a few years back, but they had no idea what a slide rule was. Like writing in script, using a slide rule is becoming a lost art...

Cheers,


Dana
 
Slide rules, because you had to keep track of decimal points, helped one develop the skill to "feel" if answers made sense.

Multiplying on them was fast; faster than doing so by hand. One could even add on a slide rule, but it was a real pain in the neck, and it was faster to add on paper.
 
My dad finished night school in the very early 60s as a production engineer. He had a collection of slide rules, From cheap wood to aluminium (with leather case) and even a long one (over 20in) he brought back from Japan after WW II (he even had a round plastic one.) When being taught to use slide rules in math in High school I used to rotate through 4-5 different ones. I once was marked down a grade on a test for carrying my answers out to the 4th decimal place. Most slide rules are only graduated to 2 places and you "interpret/estimate" the 3rd. I brought the big slide rule back into class and showed that it was graduated to 3 places and you could "interpret/estimate" the 4th place. The thing almost blocked the aisle between the desks if you had to slide it most of the way out
 
I went into the Navy in 1975, and attended the Naval Nuclear Power School at Mare Island In 1976. During that time, the rules were for all exams, you could only use a slide rule. Calculators could be used in class for non-exam situations. I think only about 25% of the class even had a calculator. I remember one guy who had a top of the line Hewlett-Packard. My first exposure to RPN.

I remember I had a pretty nice Pickett slide rule at the time. Wish I still had it.
 
swampyankee said:
One could even add on a slide rule,
Click to expand...
Depends on how you mean that. PRE-slide rule multiplying and dividing could be done the standard grade school way . However it is/was a tedious process as numbers got larger and was subject to a lot of error. One of the first things we learned in Physics and Chemistry was how to multiply/divide using logarithms. Each of us carried a pocket book of logarithms. To multiply look up the logs of both numbers, add them, do a reverse log look-up and you had your answer. Powers of 10 were in the first digit called the characteristic:
4.25 is 0.6283 and 42.5 is 1.6283 and 425 is 2.6283. Division was done by subtracting the logs. Naturally you could also mis-add or subtract but adding and subtracting were much easier.
A slide rule is just a mechanical device to do just that, i.e., add and subtract LOGARITHMS. Add one piece of stick to another piece of stick or subtract one piece from another. Thus the scales are not linear but are Logarithmic (powers of ten).
Having learned that process powers of ten were a snap 425 X 425 would be 2 + 2 = 4 characteristic and 4 x 4 = 16 so one more power of ten thus I knew my answer would be X 10^5
My best slip-stick was a Dietzgen about 18in (46cm) or so. I also had several plastic one and a circular one whose outer scales were over 3 feet long. I also had a cylindrical slide rule the opened up like a telescope. The scales wrapped around the inside cylinder and as I recall it only multiplied, divided, and had a separate scale for finding logs.
 
Dana Bell said:
Actually, the TI pocket calculators were available in 1968, when I first entered engineering school.
Click to expand...
I didn't know that. Interestingly, I had a Texas Instruments calculator when I went to JHS/HS. Years later, I went back to college and found that I was using basically the same calculator -- different year but all the features were identical (something much appreciated as I didn't have to re-learn anything).

swampyankee said:
Slide rules, because you had to keep track of decimal points, helped one develop the skill to "feel" if answers made sense.
Click to expand...
I often read tutorials online, like how to use a sextant and how to use a slide-rule and I got the sextant pretty fast, but man -- I've watched the slide-rule tutorial what the guy is describing doesn't at all match what he's doing (at least as I see it).

Shortround6 said:
When being taught to use slide rules in math in High school I used to rotate through 4-5 different ones. . . . The thing almost blocked the aisle between the desks if you had to slide it most of the way out
Click to expand...
I could imagine that thing would also be great for knocking somebody's lights out with

That's actually quite fascinating. To divide, did you just subtract the logarithm?
 
Zipper730 said:
To divide, did you just subtract the logarithm?
Click to expand...
Yup, remember your rules of exponents, i.e., 10^x times 10^y = 10^ x+y and 10^x divided by 10^y = 10^x-y
Since logarithms are just powers of 10, i.e., 425 is just 10^2.62839 and 38859 is 10^4.58949
It follows that 38859 m divided by 425 sec must be = 4.58949 - 2.62839 = 1.96110
Now do an inverse log look-up and 10^1.96110 = 91.4 (3 sig. figs.) m/s
Now remember you had to have a book with all these logs listed
 
Here's a couple for you. Gee! I hope the USAAF does not find out I got these things!
But one of their better features is that they are NOT affected by the latest Adobe Flash update!
 
Zipper730 said:
Honestly when one looks at the complexity of a slide rule: Doing long multiplication doesn't seem so hard. I'm amazed how people managed to use them
Click to expand...
I learned the "slipstick" in high school and didn't find it particularly difficult, as our teacher introduced it during our first section on logarithms. Later, as a student pilot, the E6-B came naturally, as did the CR series of round slide rules.
However, when I got around to flight instructing, digititis had taken over the schools but not yet flight training, and suddenly the E-6B and its ilk were no longer computers, but confusers. Younger students (of the digititis generation) found the E6-B harder to wrap their heads around than gyroscopic precession or the aerodynamics of P factor. Older folks had no such problem. It's all about what you grew up with.
Cheers,
Wes
 
PWR4360-59B said:
Slide rules were and are handy when there is no electricity. Complex? The old Friden and Marchant rotary calculators are very complex machines. In 72 I used one in a place I worked alot.
The best pocket calculators use RPN logic.
Click to expand...

RPN rules!

I still use the HP-15C I bought in 1985. Those silly = keys just make things messy.
 
Wow lasted that long? Are there any RPN still made now? Yeah the old rotary I had used at work was replaced with an HP45, I had bought one in the day as well.
 
PWR4360-59B said:
Wow lasted that long? Are there any RPN still made now? Yeah the old rotary I had used at work was replaced with an HP45, I had bought one in the day as well.
Click to expand...

I have that and an HP-16C, both working quite nicely. One of the casualties of Carly Fiorino's destruction of HP was the company's quality products.
 
I fiddled with an HP Reverse Polish Notation calculator for about 30 minutes....THEN I got the hammer!
Seems to me the main idea of a calculator is for the Calculator to make it Easy for me NOT the other way around
 
XBe02Drvr said:
Younger students (of the digititis generation) found the E6-B harder to wrap their heads around than gyroscopic precession or the aerodynamics of P factor.
Click to expand...
Digititis, I like that one. I suffer from it to some extent, but gyroscopic precession I get when it was explained with an old animation from the 1960's or so. You just have to remember what direction the gyro spins and from there you can determine where pushing forward or back will take you.
 
I had two slide rules from my father, who was a car tehnician. Other was a pocket size.
Great for multiplication and division, but not really anything else. Unfortunately I lost both.
My first calculator was Casio fx-17, bought in 1976. These were allowed to use in Senior High School (closest US equivalent of Finnish school system) final exams in the late 70's.

I still have this calculator. And it works !
 
mikewint said:
I fiddled with an HP Reverse Polish Notation calculator for about 30 minutes....THEN I got the hammer!
Seems to me the main idea of a calculator is for the Calculator to make it Easy for me NOT the other way around
Click to expand...

Hello Mikewint,
If you get used to working with stacks such as you might if programming in Assembly Language, then Reverse Polish seems quite intuitive.
I bought one from a Thrift Store for about $3 or so. I am guessing that it didn't sell because it didn't seem to work if anyone was expecting a normal calculator.
Heck, it doesn't even have all the same buttons!
The only real problem with it is that although it functions, the display is dim probably because the battery is low. This model has a reputation for pretty short battery life.
I have accumulated a few interesting calculators over the years.
One Casio calculator was great for my kids during their elementary school years because it could take a decimal result and give you back the fraction which is what you needed for the answer. I know that is pretty common today with the more advanced calculators but back then, it was cool and not bad for a $5 calculator from the Thrift.
The kids got a bit more advanced and I did not. As I sit here, there is a TI-83 also from the Thrift next to me. I know it works because my kids told me that it does, but I have no real idea how to use it. They use TI-84 and TI-89 Titanium for their class work and I bought one extra of those rather cool graphing calculators for Dad to use, but never found the time to learn, especially since I am not limited in what I am allowed to use on a test like they are.

I also own a slide rule with a leather case that I inherited from a relative who was an engineer. Haven't learned to use it though.

- Ivan.
 
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