# Slide rules rule!

• B
Not very modern, but straightforward to understand. He actually does the experiment and analyses the results right in front of you.
Digression, but what on Earth is that ruler thing he's using to calculate products at 14:10 and 15:40?

Edit: I found it, it's called a "slide rule":
https://www.math.utah.edu/~alfeld/sliderules/

hutchphd, DaveE, Ibix and 2 others

Homework Helper
Gold Member
Digression, but what on Earth is that ruler thing he's using to calculate products at 14:10 and 15:40?

Edit: I found it, it's called a "slide rule":
https://www.math.utah.edu/~alfeld/sliderules/

possibly useful: https://www.sliderules.org/ virtual slide rules

possibly interesting:

updated link to the article on Symmetry:
https://www.symmetrymagazine.org/article/december-2005january-2006/artifact-relativator

Last edited:
Janosh89, Ibix and etotheipi
andresB
Digression, but what on Earth is that ruler thing he's using to calculate products at 14:10 and 15:40?

Edit: I found it, it's called a "slide rule":
https://www.math.utah.edu/~alfeld/sliderules/

Pretty ingenious, but thank gods for computers.

etotheipi
Gold Member
Seriously, there is one great thing about slide rules. They only give you the mantissa, and just a few significant digits at best. This forces people to actually think about the calculation; built in error checking. An electronic calculator is quite capable of giving erroneous answers if you make a mistake (so will a slide rule), but people don't always do a sanity check. There is some value in using your brain to get a rough answer, before the machines give you a more exact solution.

BTW, my circular slide rule got me through High School Chemistry class and was then permanently retired, it now sits in a box of mementos.

symbolipoint, anorlunda and Sagittarius A-Star
Mentor
Hold on to your slide rules folks when the EMP comes you'll need them to rebuild civilization. :-)

SammyS, OmCheeto, coolul007 and 4 others
jedishrfu and robphy
Staff Emeritus
Gold Member
Not a slide rule, but an old style "flight computer".

jedishrfu

### Slide Rule vs Calculator Showdown: Decilon & HP-35​

FactChecker
Gold Member
Hold on to your slide rules folks when the EMP comes you'll need them to rebuild civilization. :-)
I'll just get some bamboo and make one.

jedishrfu
Gordianus
I'm old and I've used slide rules. I remember the cheap, small models (5" long and a few lines). The "monsters" were about 12" long, 3" wide and had lots of lines. Quite useful (50 years ago). Perhaps, the last great survivor of the "analog" era is the Smith chart.

jedishrfu
Mentor
Mentor
I've got about six slide rules here at the house. Back when I first started college, there were no pocket calculators, so calculations were done using slide rules exclusively. About 10 years later, HP came out with the HP-35, which cost about USD300, and they still go for close to that.
They only give you the mantissa, and just a few significant digits at best. This forces people to actually think about the calculation; built in error checking. An electronic calculator is quite capable of giving erroneous answers if you make a mistake (so will a slide rule), but people don't always do a sanity check. There is some value in using your brain to get a rough answer, before the machines give you a more exact solution.
Or an "exacter" solution. Forcing people to actually think about the calculation is a good thing; otherwise it's garbage in, garbage out.

Mentor
I did my physics lab with a combination of sliderule math and adding machine math.

In some cases, i converted my data to logs, added things up and converted back to get a few more digits of accutacy.

Gold Member
Then there's this mechanical calculator first made by someone when being a prisoner in a nazi concentration camp:

https://en.wikipedia.org/wiki/Curta

Too bad that nowadays senior high school students are not even shown how to calculate approximations for irrational square roots by hand without a calculator. Except in some East European countries where there's more advanced math at that level of schooling.

jedishrfu
Mentor
Scientific American did an article on these incredible devices.

https://www.scientificamerican.com/article/the-curious-history-of-th/

I recall someone saying you could never repair them because once you opened it the springs would escape and there was no chance of putting it back together.

i always wanted to own one but they were always way out of my budget even now.

They were also known as a pepper grinder because of their shape and the need to spin a handle.

Gold Member
I did my physics lab with a combination of sliderule math and adding machine math.

In some cases, i converted my data to logs, added things up and converted back to get a few more digits of accutacy.
That's nothing. I had to use an abacus and record intermediate results on a clay tablet with a stylus.

Jack of some trades, anorlunda, jedishrfu and 1 other person
Gordianus
Does someone remember nomograms?

Tom.G and anorlunda
That's nothing. I had to use an abacus and record intermediate results on a clay tablet with a stylus.

Lucky bastid! We could only dream of having a stylus

jedishrfu and Keith_McClary
2021 Award
i always wanted to own one but they were always way out of my budget even now.
I find the details of computational instruments fascinating.

I keep a Curta on my desk, to remind me of that tragic past. My slide rules are in the draw, where their batteries won't go flat. There is a box of retired HP RPN calculators somewhere in the store. I keep a HP 48G under my pillow.

My Original Odhner LuSiD is good for 10 digits. I gave it a full service and taught myself to calculate square roots on it when it was over 80 years old. I now take it to "show and tell" events where I get to demonstrate what very few people have seen.
http://www.vintagecalculators.com/html/odhner_lusid.html

Tom.G and Keith_McClary
Staff Emeritus
Very nostalgic.
Does someone remember nomograms?
Ah yes. In my M.E. courses, we learned to make our own nomograms. Some of the homework assignments were difficult. You can be very creative about the position, and angles of the scales, and even use curved scales.

It might be fun to do that today. I wouldn't be surprised to see an online calculator that could do it for you. Young people might be fooled into thinking that it was a new invention.
Hold on to your slide rules folks when the EMP comes you'll need them to rebuild civilization. :-)
My Post slide rule came with a high quality leather sheath that could be worn on the belt. I still have it. Back then, there was a big social stigma about wearing it on your belt; very nerdy. Wearing it today might get you shot by police who think it must be a weapon, but at least you would have it with you when the EMP comes.

I also remember raging debates among engineering students about which was best, Pickett (metal) or Post (bamboo). My boss owned a one meter long Pickett slide rule. He claimed to be able to get one more significant digit in his results.

Gold Member
... slide rule came with a high quality leather sheath that could be worn on the belt.
In the campus lost-and-found they had a big bin of those, much better than my little bamboo model in the tattered cardboard box.

anorlunda
Mentor
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hilbert2
Staff Emeritus
jedishrfu
Don't forget a backup method to make your PF posts.
That should be possible with a Z1 computer.

anorlunda
Mentor
Except the Z1 is electro-mechanical and an EMP might still knock it offline.
In 1962, the USA carried out a nuclear EMP experiment in high altitude near Hawaii:
Wikipedia said:
Starfish Prime caused an electromagnetic pulse (EMP) that was far larger than expected, so much larger that it drove much of the instrumentation off scale, causing great difficulty in getting accurate measurements. The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about 900 miles (1,450 km) away from the detonation point, knocking out about 300 streetlights,[1](p5) setting off numerous burglar alarms, and damaging a telephone company microwave link.[6] The EMP damage to the microwave link shut down telephone calls from Kauai to the other Hawaiian islands.
Source:
https://en.wikipedia.org/wiki/Starfish_Prime

I think, that electro-mechanical relais are more robust against EMP than transistors or integrated circuits, because their wires have a larger diameter, and so the current density is lower. Solid state equipment has a problem:
Wikipedia said:
Older, vacuum tube (valve) based equipment is generally much less vulnerable to nuclear EMP than solid state equipment, which is much more susceptible to damage by large, brief voltage and current surges. Soviet Cold War-era military aircraft often had avionics based on vacuum tubes because solid-state capabilities were limited and vacuum-tube gear was believed to be more likely to survive.
Source:
https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse#Vacuum_tube_vs._solid_state_electronics

On the other hand, computers with smaller size collect less voltage from a certain electric field. So smartphones may work:
Wikipedia said:
An EMP has a smaller effect the shorter the length of an electrical conductor; though other factors affect the vulnerability of electronics as well, so no cutoff length determines whether some piece of equipment will survive. However, small electronic devices, such as wristwatches and cell phones, would most likely withstand an EMP.
Source:
https://en.wikipedia.org/wiki/Nuclear_electromagnetic_pulse#On_small_electronics

emmawarner96
The slide rule is often used for multiplication and division, but it can also be used for functions like exponents, roots, logarithms, and trigonometry. It is rarely used for addition or subtraction.

The introduction of the inexpensive, fast, and versatile electronic pocket calculator led to the slide rule's demise.
The owner's slide rule used to have a special status, but that was happily replaced by the equally special status of the dazzling HP-35.

2021 Award
The “General Report On Tunny With Emphasis On Statistical Methods” (1945) from Bletchly Park, GCCS, includes the following inventory item and comment;

“Section 57. Simple Machines.
(a) Slide-rules.
The operations required are multiplication, division, squaring, extracting square roots, and taking logarithms to base 10. Many of the slide-rules used lack logarithms, and have elaborate useless scales.”

Obviously the scales A, B, C & D had no meaning to the author, while the L scale on the rear was not Log because it was Linear !

Keith_McClary
Staff Emeritus
Obviously the scales A, B, C & D had no meaning to the author, while the L scale on the rear was not Log because it was Linear !
Ah the nostalgia. You motivated me to take down my old Post from the wall to see what scales it had. When I used it actively, I knew the purpose of all those scales and I found productive uses for them.

Here are the scale labels:

ex LL0 0.001→0.01
e-x LL/0 -0.001→-0.01
K
DF
CF
CIF
CI
C
D
R1
R2
L
e-x LL/1
e-x LL/2
e-x LL/3

T T
sec T ST
Cos S
e-x LL/1 -0.01→-0.1
e-x LL/2 -0.1→-1.0
e-x LL/3 - 1.0→-10.0
C
X D
ex LL1 1.0→10.0
ex LL2 0.1→1.0
ex LL3 0.01→0.1

Keith_McClary
Mentor
That's nothing. I had to use an abacus and record intermediate results on a clay tablet with a stylus.

Lucky bastid! We could only dream of having a stylus
Luxury! We could only count on our fingers...

Staff Emeritus