
Illustrated Self-Guided Course On How To Use The Slide Rule - ngram
https://sliderulemuseum.com/SR_Course.htm
======
philiplu
What a blast from the past. I can draw a direct line from my encountering a
slide rule to ending up as a programmer. I owe my career to that device.

I was a nerdy 10 year old kid who liked doing arithmetic in 1970, but didn't
know anything particularly advanced. I convinced my parents to get me a slide
rule as a Christmas present that year; a basic white Post model 1447 - I know
that because I'm looking at it right now. It's been in my desk drawer forever
as I could never convince myself to throw it away, even though I've long since
lost the sliding cursor.

Anyway, I got the slide rule, had fun with basic multiplication/division, but
didn't understand what the S, T, and L scales on the back were for.
Sine/Tangent/Logarithm? What are those?

Off to the library, where I picked up a Tutor-Text book [0] on trigonometry,
discovered I'd better first learn some algebra, picked up another Tutor-Text
book on that, and began a two-year tear teaching myself algebra to integral
calculus. Which meant I tested out of a couple years of math in high school,
ran out of courses to take, and in my junior year was allowed to walk to the
local college to take 2nd year Calc classes.

At that college, they started letting me play with the computers, both an IBM
5100 APL machine over one summer, and hands-on access to the IBM 11/30 clone
minicomputer that was the main machine. The math prof pointed me at Knuth's
"The Art of Computer Programming", and that began my transition from pure
mathematics to computer programming/science instead. I even wrote a MIXAL
assembler/MIX simulator for the minicomputer that the college ended up using
to teach an assembly language course.

So thank you, Post, Pickett, K&E! And Tutor-Text as well.

[0]:
[https://gamebooks.org/Series/457/Show](https://gamebooks.org/Series/457/Show)

~~~
gonzo
Similar background story, I was 8 in 1970, and my father knew what a slide
rule was, and how to use it, so I learned a bit of trig from him before
repeatedly checking out a textbook on trig from the public library.

True story: my son took an AP physics class in high school, (LASA) taught by
sokeone with a PhD in physics. They had an oversized teaching sliderule
hanging from the ceiling, where nobody could use it. It had become decoration,
as nobody was left to teach with it.

When I was at the school for a “meet your student’s teachers” night, one of
the other parents asked about the side rule. Instructor didn’t know how it
worked.

So I explained it.

My wife still has her grandfather’s slide rules from when he was the state
engineer in the 50s and 60s.

~~~
philiplu
I remember those large teaching slide-rules, but haven't seen one in decades.
Great to know they still exist, if only as mysterious artifacts from the dark
ages.

Neither of my parents were mathematically inclined, but they were content to
let me forage for information on my own, with lots of trips to the library.
Amazing how clear are my 50-year-old memories of 10-year-old me sitting on the
floor with a trig book, drawing random triangles on paper, measuring them as
carefully as I could with ruler and protractor, and verifying the law of sines
and cosines with paper and slide-rule. God, I was such a nerd. Paid off well
in the end, though :-)

Now I'm retired, and for fun, I work my way through the problems at Project
Euler. Four years in, and only two more problems to go to hit 90% complete!
It'll probably take me another year+ to finish them all (hopefully).

~~~
thechao
We end up doing a lot of back-of-the-envelope calculations for various odds-
and-ends. I keep a 4’ long teaching slide-rule next to my desk for this
purpose. New employees are befuddled. Everyone else just accepts it as a fact-
of-life when asking for my help.

------
derekp7
One under-appreciated aspect of a slide rule, is for instantly seeing fraction
reductions at a glance. For example, lets say I want to find out what aspect
ratio a given screen resolution is at. I can set that resolution as a ratio on
the slide rule's C/D scales (i.e., 1680x1050 becomes 1.68 one C, lined up with
1.05 on D. Then I glance over, and see immediately that is 16 x 10
resolution.) If the value goes off the scales, look up to the CF/DF scales.

This is also great when you have a bunch of resistors and capacitors, and you
need to build a circuit where the two are at a particular ratio. Set the ratio
you want, then you can take whatever resistor you have, and see if you have a
cap that is "close enough" to what you need.

~~~
kqr
Also ratio multiplications, e.g. when increasing the amounts of ingredients in
recipes to match a particular amount of something.

So if the primary ingredient is chevre cheese, the recipe calls for 180 grams,
but you can only buy it in 250 gram packages, you can set the slide rule to
"180 over 250" and then just mechanically read off the proportionally correct
amounts of all other ingredients.

Slide rules are indispensable in the kitchen to me and I'm surprised they're
not part of standard kitchen equipment like e.g. scales.

Edit: Similarly, if the recipe is expressing ingredients in US units and you
would want to know the international amounts, you can set the slide rule to
the conversion ratio and again, mechanically read off the correct amounts as
you go.

~~~
gumby
This is one advantage of the customary (English language non-metric) units:
the common ones are full of rational factors (1/2, 2/3 etc) — it’s pretty easy
to adjust a recipe to the number of people.

------
ColinWright
A few years ago I met Fred Haise Jr and got him to sign one of my Slide Rules.
He was so excited to see it, took it from me, and started to show the event
host how to use it!

He asked me what I use to lubricate it, and when I said "Pencil graphite" he
got even more excited. Apparently a lot of the other astronauts had used fancy
light lubrication oils, but he always used a pencil and never had any
problems.

He was a lovely man, and it was fabulous to enthuse with him over this
wonderful piece of technology.

~~~
mcguire
Powdered graphite is an excellent lubricant that doesn't attract crud. My
father had a little squeeze tube of it for locks; it eventually ran out and I
haven't seen any more since.

~~~
philiplu
You can find the small tubes at hobby stores, with the supplies for Pinewood
Derby cars for Cub Scouts. I went through several tubes during my son's years
in Scouts.

~~~
avhon1
You can also get it at hardware stores for lubricating locks.

~~~
EricE
The versions for lubricating motorcycle cables are finer and less messy than
the cheap stuff they sell for locks. If you want to be neater with your slide
rule, anyway :)

------
xenocyon
As someone who grew up in India in the 20th century: slide rules are
unfamiliar, but we used log tables (calculators of any kind were prohibited
through high school and standardized tests). For those unfamiliar, log tables
serve to replace multiplication/division of floating-point numbers with
addition/subtraction instead, making scientific computation a lot easier.

The main benefit of introducing this friction, rather than allowing
calculators, is that it (a) encourages one to do simple calculations by hand,
and (b) gets one in the habit of quickly double checking that log-table-based
results fall in the correct ballpark. Calculators induce a sort of
mindlessness where glaring orders-of-magnitude errors pass us by since we
expect the machine to get it right.

With all that said, I don't know that I would recommend the use of log tables
to high schoolers in the 21st century. That effort might be better utilized on
more pressing needs e.g. statistical literacy. Many folks (including me) got
entirely through STEM-focused high school knowing not even the slightest
basics of statistical inference or causality.

~~~
metiscus
I think that learning how to use a log table might cement certain
relationships for more advanced students. But I do agree that in general there
are probably better uses of one's time than to teach them as a first class
citizen.

------
drfuchs
Another great thing about slide rule days is that results are naturally
constrained to 2 or 3 significant digits, so you'd never see nonsense like
"The mountain is 10km high, or 32808.4ft" as if the 10km figure was accurate
to 6 significant digits.

~~~
sirsar
I still remember the day I found out the "98.6 degrees" human body temperature
was just an oversignificant conversion from "about 37 C, or maybe lower."

~~~
JadeNB
> I still remember the day I found out the "98.6 degrees" human body
> temperature was just an oversignificant conversion from "about 37 C, or
> maybe lower."

Really? According to Wikipedia, the Fahrenheit scale
([https://en.wikipedia.org/wiki/Fahrenheit#History](https://en.wikipedia.org/wiki/Fahrenheit#History))
is about 18 years older than the Celsius scale
([https://en.wikipedia.org/wiki/Celsius#History](https://en.wikipedia.org/wiki/Celsius#History)),
and I'm surprised that human body temperature wasn't included as a
calibration. (But of course the fact that I'm surprised by it doesn't mean it
isn't true!)

~~~
cyphar
Fahrenheit was initially intended to have 96°F be equal to body temperature
(in fact it was one of the three fixed points in the temperature scale,
designed to have 64 steps between the freezing point of water at 32°F and
human body temperature).

However after the introduction of Celcius, Fahrenheit was redefined slightly
(with the freezing and boiling point of water being the fixed "nice" values
for the scale -- to match the model used by Celcius) which resulted in human
body temperature no longer having such a nice value. This also moved the 0°F
value. So while technically Fahrenheit does predate Celcius and it did have a
"nice" value for body temperature when invented, it was soon afterwards
redefined such that arguably the value is just a conversion from Celcius.

In short, you're both correct. :D

~~~
folli
Why did they come up with 96 instead of 100, a nice round number?

~~~
jcranmer
Imagine you've just made yourself a thermometer by marking off the 0° and 100°
points. Now delineate the 2° intervals, using only the tools you would have
had available in the early 18th century.

Now imagine making a thermometer by marking off the 32° and 96° points (64°
apart). Now delineate the 2° intervals.

Considering those two tasks, 64 seems a much better number to me (only have to
divide unit lengths in half) than 100 (have to divide something by 5).

~~~
folli
Great explanation, thanks.

------
KineticLensman
Alas! No specific mention of the circular slide rule [0]. I have one in my
desk drawer that I inherited from my dad - who used it in the 1970s to confirm
his hip hacker credentials to his colleagues (they were building the control
circuits for early radio-therapy machines in a cancer research institute).

[0] [https://americanhistory.si.edu/collections/object-
groups/sli...](https://americanhistory.si.edu/collections/object-groups/slide-
rules/circular-slide-rules)

~~~
dan-robertson
Circular slide rules tend to have smaller scales which may be harder to read
but being circular has a great advantage. Look at how much effort in the OP is
devoted to cases where the answer would ordinarily be off the end of the
scale.

------
ghaff
Slide rules to calculators was an incredibly fast technology transition for
the sort of people who would have been using slide rules in the first place.

A 5-function calculator was about $100 in 1974 (so about $350 in current
dollars) and an HP scientific calculator was 3 or 4x as much. By about the
next year, a TI scientific calculator was about the same and by a year or two
later you could get an HP--which was the gold standard for about the same
amount.

And that was around the price point where making them not just OK to use but
mandatory was reasonable at least in higher ed. I was one of the first classes
in college where calculators were the norm and slide rules were maybe
something you brought for backup at exams. (Calculators were still LEDs so you
had to keep them charged.)

------
stblack
One of the nicest things about a slide rule is, you can easily see the
sensitivity of the result to variations of your last input.

With a calculator, you get precision. With a slide rule, you get a value and
its sensitivity.

------
tzs
One unexpected advantage in some circumstances of a slide rule over current
portable computing devices is that it does not have memory.

You are allowed to bring a calculator to ham radio license exams in the US,
but you have to clear its memory (both data and program memory for
programmable calculators) first. If the examiners aren't sure you have done
so, they are supposed to disallow the calculator.

Unlike many other standardized tests, there is no specific list of what
calculators are allowed. I brought my HP-15C, but wasn't sure that the
examiners would be familiar with it and so wasn't sure I'd be able to convince
them that I had cleared it.

I also brought a slide rule. That way if the examiners disallowed my HP-15C
I'd still be covered.

They did allow the HP-15C, and it turned out that even though I took all three
exams (Technician, General, and Extra) that day, I only actually used the
calculator once. The questions are all multiple choice, and there was only one
where a quick mental approximation wasn't enough to identify the right answer.

~~~
Someone
Nitpick: a slide rule _does_ have memory, but it is small and gets cleared
when doing computations. One typically can store one number by moving the
slide and another one by location of the cursor.

It also is fairly hard to hide the fact that the memory isn’t cleared.

Many slide rules also have some read-only memory, for example ’storing’ the
constant π.

------
code4tee
The “E6B Flight Computer” is a slide rule designed to perform various
navigation calculations and is still a part of flight training for many pilots
today. Once mastering it the old way student pilots are then allowed to use
electronic versions or iPad apps that do all the calculations instantly.

------
bregma
When I was in university, if you forgot your slide rule at an exam they kindly
had a supply of log tables you could pick up from the proctor.

------
wdb
Cool, now I finally know how to use this rule that I got when me and my
siblings were clearing up the family house after my parents passed away.

It's really fascinating, I will show my nephews when I am back in the home
country :)

Thanks for posting!

------
leetrout
Circular slide rules are still used today in aviation in the form of the E6B
flight computer.

[https://en.m.wikipedia.org/wiki/E6B](https://en.m.wikipedia.org/wiki/E6B)

~~~
ghaff
Back when slide rules were still widely used and even after calculators had
recently come in, you also saw a lot of industry-specific cardboard sliding
scales that were basically slide rules with different types of units.

------
ashton314
Oh this is wonderful. I first learned about slide rules from a math teacher
back in junior high. I wasn't until a few years after that that my little
sister gave me a slide rule for Christmas. \o/

After graduating high school I spent two years in Germany. Whenever I found a
flea market or an antique store, I'd search for slide rules. I found two that
were in pretty good condition. People always seemed a little confused as to
why I wanted these. I guess they just didn't see the beauty in these simple,
elegant devices.

------
ssimpson
I've been trying to figure out how to use my grandfathers Dietzgen Maniphase
Multiplex Decimal Trigtype Log Log rule. I found the manual on this site! Very
cool!

------
reaperducer
I'm old enough that I had a slide rule when I was in school. Everyone did.
They were built in to our pencil boxes.

Most of us didn't use them, except the fancy-pantses who also insisted on
using mechanical pencils. But we all knew how to use them.

I'm graybeard enough that even through college, electric calculators were
prohibited in class because they would give you answers without helping you
understand the problem.

~~~
qrbLPHiKpiux
> answers without helping you understand the problem

This is my problem with common core math. It shows how to get to an answer,
but I feel it bypasses fundamental understanding on why the answer is what it
is.

~~~
metiscus
I feel that common core focuses more on teaching the various methods than
embracing the idea that correct answers and understanding are largely what
matter rather than any specific method.

~~~
JadeNB
> correct answers and understanding

It's natural to lump these together as if they are a unit, but I think it's
important to be explicit about the fact (which of course you know) that they
are all too easily separable: it is incredibly easy, given sufficiently
powerful tools, to get correct answers with little to no understanding. True
understanding (not just "oh, I think I get it") that doesn't help to get
answers is not nearly as common, but of course it exists, too.

~~~
metiscus
Yes I totally agree with your sentiment that it is vitally important to
separate the correct answer from the method by which it is achieved. Honestly
understanding mathematics is more important at some level than getting the
right answer to a particular problem. That's the whole point, once you
understand the grammar and vocabulary of mathematical thinking you can attempt
to solve problems that are totally unrelated to things you know and still
sometimes get useful results. The overwhelming question of the ages is how do
you teach with that goal in mind and take account of all of the different
learning pathologies while doing it in a universally accessible and measurable
way. I think the problem is intractable as it is currently being approached.

------
dave_aiello
In an era marked by renewed interest in vinyl records, shouldn't there also be
a corresponding interest in slide rules?

~~~
coldpie
I dunno, man. I'm pretty well-versed in math and I find this page kind of
baffling. I'm sure it's one of those things that is very easy to use once you
learn it, but at least this introduction is very daunting. To do a basic
multiplication (step 1 in the linked page) I need to use the C and D scales,
each for two different purposes. Why not A and B? How do I remember it's C and
D? Which part goes on C and which part goes on D? Then step 2 describes what
to do if it goes off the edge of the scale, and it involves making an
approximation. How do I know how accurate my approximation must be? Why is it
to the tens digit? If I get larger numbers do I continue to use the tens
digit, or some higher factor? We're only on step 2 and I'm already lost.

This definitely looks like a great tool, and I'm kind of sad I don't have one
or understand how it works, but this kind of complex learning and memorization
up against dropping a needle on a record you like isn't really a great
comparison.

~~~
yuubi
It works better if you know how the scales are constructed and get familiar
with properties of logarithms (mainly variations on log ab = log a + log b)

C and D are plain log scales, where one decade is the length of the rule.
They're sort of the default scales to use.

Multiplication is commutative, so you put either number on either scale. The
important thing is that the distance from the left index of the scale is
proportional to the log of the number (reading the scale as 1 to 10), so you
want to arrange the scales to add the lengths corresponding to your numbers
such that the lengths add up. (Or so that you subtract the length of the
divisor from the dividend, if you're dividing).

You can get by without the approximation if you're willing to set up the
multiplication, see that the product is out there in thin air, then move the
slide to put the right index where you originally put the left index. (3 times
5: on the d scale find 3 and put the left index of the C scale there; opposite
5 on the C scale read nothing because there's no D scale there; try again
using the right index of the C scale, which is the same thing as having
another copy of the D scale out there to the right where the air was).

A and B are each 2 copies of a log scale. You can absolutely use the left side
of A and B for your numbers to multiply, and the product will always be on the
scale.

People normally use(d?) C and D because the precision is better and because
the rest of the scales (like the trig and log-log) are constructed to work
with them.

~~~
kqr
Nit: while multiplication is commutative, the property you meant to use was
symmetry. I'm sure it was a mistake and you know this, I'm just pointing it
out to prevent confusion for others.

Edit: s/competitive/commutative/

~~~
jstanley
[https://en.wikipedia.org/wiki/Commutative_property](https://en.wikipedia.org/wiki/Commutative_property)

> In mathematics, a binary operation is commutative if changing the order of
> the operands does not change the result.

Are you saying you disagree?

~~~
kqr
No, I had a brainfart and was thinking of associativity. I have no idea how it
happened. Very embarrassing.

------
veddox
Our math teacher, a former engineer, once brought his slide rule to class when
we were in grade 9. He posed a problem and raced us to the solution, slide
rule vs. calculators. He beat us all...

------
lebski88
I actually spent a bit of time learning about Slide Rules a few weeks ago as
my Dad had put together a very cool interactive slide rule in JavaScript that
I wanted to have a play with.

[https://adit.co.uk/sliderulev2.html](https://adit.co.uk/sliderulev2.html)

One thing that struck me was that it does require a good instinct for the
magnitude of numbers to use. Lots of fun though and surprisingly quick to use.

------
sizzzzlerz
Simply put, I love a slide rule. My dad gave me mine for my 17th birthday, 48
years ago and I’ve treasured it ever since. It’s the Pickett trig model and it
served me well into my 3rd year of college as a EE. Its simple to use after
you’ve been trained and totally reliable. It can also be quick as your skill
using it develops. It sits in a drawer today but I take it out occasionally to
play with. It truly is like a friend.

------
throw0101a
There's a 'Professor Herning' whose YouTube channel has both good tutorials on
their use, as well as comparing many models (and the various scales they
have):

* [https://www.youtube.com/c/ProfessorHerning/videos](https://www.youtube.com/c/ProfessorHerning/videos)

------
4x5-Guy
Being in Junior College in 1973, some of the kids had 4 function calculators
hanging off their belt. The rest of us in a tech track usually carried a slide
rule.

I did take a technical math class that involved programming a desktop
calculator. Basically the first programming class I had.

I wish I remembered what brand it was, I'd like to try to pick one up if I
could find one.

------
supernova87a
I think practice with a slide rule also gets you to sanity check your method
and think whether the answer can be correct.

Given how you could forget and inadvertently reverse the scales, etc, you have
to think whether the answer you're getting makes sense by looking at the trend
of the numbers. Plug and chug into a calculator takes some of that away.

------
lokedhs
I'm of the generation that missed out on slide rules by a decade or so. My
parents had one thta i played with as a kid, and I learned to do
multiplicication and division with it.

I'd like to get one now, mainly for fun, but if you want to buy one on Ebay in
good condition, you have to pay quite a bit of money.

~~~
ghaff
Plastic "student" slide rules are cheap on eBay. But, yes, quality K&E's etc.
are expensive.

~~~
lokedhs
Since this is something I want to keep on my desk, not only for decoration but
for actually copute things if I'm bored, I really want tone of the nicer ones.

It seems around 35 EUR is a normal price.

~~~
ghaff
Quality slide rules probably cost a lot more than that when they were still
being manufactured :-)

------
dylan604
One of my favorite scenes in "Apollo 13" has a CO2 hazy Jim Lovell asking
Houston to double check his math, and it cuts to a room full of engineers as
they all grab their slide rules to calculate the answers Jim had just done in
his head/scratch pad.

------
markbnj
My Dad, an engineer for GM/Cadillac, gave my brother and I each a slide rule
back in the 60's. I remember marveling at the precision of it, and I did learn
to use it for some calculations, but not to a level that impressed him :).

------
watersb
I love playing with slide rules because it wraps my brain into using
logarithms everywhere.

The game of Go also redecorates my thinking, in a way I cannot put into words.

Slide rules!

------
ogogmad
Also check out the quarter-square method and prosthaphaeresis.

------
agumonkey
Fascinating near invisible yet very high abstraction.

------
surajs
how eccentric! would much rather prefer a yt vid / tutorial pls.

~~~
toolslive
I think the preference is age related: Personally I prefer text over video, as
I can process it at my speed, while with video I'm limited to the speed with
which it's explained.

My children all seem to prefer video.

~~~
JadeNB
> I think the preference is age related: Personally I prefer text over video,
> as I can process it at my speed, while with video I'm limited to the speed
> with which it's explained.

> My children all seem to prefer video.

When I ask for text transcripts of our training videos, in place of having to
sit through 20 minutes of poorly acted out skits (that, re-certification being
a periodic thing, I have sat through some 5 or 6 times already in my 10 years
on the job), I am always told "but people enjoy the videos"—as if providing
transcripts were somehow exclusive of providing videos.

