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Author Topic: Can someone teach me to use a slide rule please?  (Read 5860 times)

RipSlider

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Can someone teach me to use a slide rule please?
« on: August 26, 2008, 09:34:13 pm »

I have a job coming up where electronic security is incredibly tight. I'll be locked in a room for 8 hours a day and allowed no digital devices of any kind as I'll be dealing with some fairly sensitive data, and so i can't even take in a calculator. I also have to walk through an airport scanner thingy and a massively powerful magnet just to make sure.

Anywho, in getting ready for this job, I realise that I'm going to have to do some sums - lots of multiplication and division.

I could do it all long hand, but this doesn't seem very productive. So I was thinking that a slide rule might be useful. The problem is that I don't actually know how to use one.

I have read a few tutorials on the web, but they don't make a lot of sense to me.

I was wondering if anyone here has used on and could give me a bit of a crash course, preferably with a couple of worked examples.

However, I can't take in any books etc to the job either, so if I need log tables to use a slide rule, then the plan is not a good one.

<<I'm not sure WHY I think log tables are involved. I'm sure the old man used to use a slide rule with log tables, but I have no idea what he was doing with them>>


Ta

Steve
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Colin Bishop

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Re: Can someone teach me to use a slide rule please?
« Reply #1 on: August 26, 2008, 09:37:21 pm »

Wrong job Steve, get another one.
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andyn

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Re: Can someone teach me to use a slide rule please?
« Reply #2 on: August 26, 2008, 09:38:36 pm »

Get in touch with the bloke who owns this website http://www.stefanv.com/rcstuff/, He collects them ???

I built his tachometer for my GCSE tech project.
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Rex Hunt

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Re: Can someone teach me to use a slide rule please?
« Reply #3 on: August 26, 2008, 09:48:46 pm »

take 25x30 as an example.          :-\

line the 1 of the slide up with 2.5 on the scale......
move the cursor slide so it passes through 30 on the slide and read off on the main scale.

to divide 30 by 2.5

put cursor over 30 on the upper scale,
line up 2.5 on the slide with the cursor.

move the cursor over the 1 on the slide

read off on the main scale.     O0

hth

Rex
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #4 on: August 26, 2008, 09:51:31 pm »


It's been 40 years, but if I remember...

You align the zero mark (or as Rex has it, the 1)? on the sliding scale with one of the numbers you are multiplying on the fixed scale.  Then look for the second number you are multiplying on the sliding scale.  The answer is where the second number that you are multiplying aligns with the fixed scale.  Fractions are calculated by seeing which two marks align - rather like a micrometer.

You then take a guess at to the power (x10, x100)etc. - or at least i did {-) {-)

The scales on a slide rule are logarithmic, and not linear.

Malc

 
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #5 on: August 26, 2008, 09:53:33 pm »

Posted in error
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JayDee

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Re: Can someone teach me to use a slide rule please?
« Reply #6 on: August 26, 2008, 10:16:28 pm »


Hello,

 A Slide Rule, if it is any good, WILL be made of metal !!!.
Never seen a plastic one, but used lots of METAL ones.

John.
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #7 on: August 26, 2008, 10:42:31 pm »



Rex's memory is better than mine - or at least his explanation of how to use a slide rule is...

I think mine is still up in the loft?  It's a plastic one, made by Faber Castell.

Malc


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dougal99

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Re: Can someone teach me to use a slide rule please?
« Reply #8 on: August 26, 2008, 10:43:18 pm »

My Dad's slide rule was plastic but the cursor glass had a metal rim. Rip you'll have to use an abacus.  ::)

We had a little revolt at school in the upper sixth when we found out that whilst we were using Napier's Tables the IV form were allowed slide rules. Blo ody technology  >>:-(

Doug
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roycv

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Re: Can someone teach me to use a slide rule please?
« Reply #9 on: August 26, 2008, 11:13:49 pm »

Hi its just a thought but if they expect you to use a calculator to do the work, why not ask them to supply you with appropriate calculating abiility, you do the work and then hand it back.
regards Roy
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sweeper

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Re: Can someone teach me to use a slide rule please?
« Reply #10 on: August 26, 2008, 11:23:21 pm »

As stated above, when you use a slide rule you are, in effect, using log tables.
Principle of use for logs, add the logs together to multiply, subtract the logs to perform division. A slide rule does this mechanically for you.

Most of the slide rules are 10" wood or plastic. 5" versions are available to carry in your pocket (not so accurate in use) or if you can find one, a tubular version with the scales wound in a helix to give about a 40" slide rule equivalent (very accurate) but with a knurled metal cap it would not match your needs.
I once got to play with a six foot slide rule (in a marine design office), what a toy that was!
And yes, even though I have had a caclulator since 1973 (several in fact), I still carried my slide rule in my bag at work. At least you never have trouble with the battery going flat!
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grasshopper

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Re: Can someone teach me to use a slide rule please?
« Reply #11 on: August 26, 2008, 11:28:35 pm »

try googling slide rules, I did - try this
http://www.sliderules.info/

If you want a slide rule instruction book I have one (with the Faber Castell slide rule) - and I could probably manage to scan it and email it.
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SteamboatPhil

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Re: Can someone teach me to use a slide rule please?
« Reply #12 on: August 26, 2008, 11:34:53 pm »

I still use my slide rule in the workshop, and (sadly) most of it still comes naturally, although had to resue it not long ago as my son was using it just to draw straight lines with !!!! >>:-(
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Bunkerbarge

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Re: Can someone teach me to use a slide rule please?
« Reply #13 on: August 26, 2008, 11:54:03 pm »

One thing that has not been mentioned which I remember well from school is that the first thing you do with a slide rule calculation is an estimate in your head.  This is simply to determine where the decimal point should be in the final answer as the scales are nothing more than log scales.  They do not contain decimal points so the 2 you use on the lower scale could relate to 2, 20, 200 or 20,000!!!

So a quick estimate in your head is essential before starting.

I must admit this sounds like a really weird job though, I'd tell them to do thier own sums!  I also remember from my own slide rule that it was plastic with a clear plastic cursor carrier which had a metal leaf spring in it to ensure alignement.
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andrewh

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Re: Can someone teach me to use a slide rule please?
« Reply #14 on: August 27, 2008, 08:24:52 am »

I still have several and use them as required - the batteries never go flat on a slipstick

Where are you in the world?  It is a lot easier to show you than describe it, and there are basically only two actions - multiplying and dividing (and they are actually both the same)  Happy to meet up if this is physically possible and show you  - I have several straight and circular rules

What a learned and helpful forum ;D - as several people have said they are logarithmic scales and so multiplying is adding lengths, and dividing subtracting them.

BB is dead right - they tell you the number of the answer but not the size.  It is ESSENTIAL to make a rough calculation to determine where the spot comes - but you would do that anyway wouldn't you?

andrew
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RickF

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Re: Can someone teach me to use a slide rule please?
« Reply #15 on: August 27, 2008, 09:40:44 am »

I read this thread with interest, then went to find my old slide rule - a plastic Faber Castell. Finally located it in the bottom of a box of old model railway junk, where I think it has been since I finished my apprenticeship in 1964. Unfortunately, the cursor is long gone. However, sliding the rule open revealed all the cribbed formulae I had written inside 45-odd years ago in an attempt to pass my ONC. If only I could remember what they mean!

Rick
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Re: Can someone teach me to use a slide rule please?
« Reply #16 on: August 27, 2008, 04:25:10 pm »

Tut, tut, RickF.
That's being naughty ain't it? Writing on your rule.... :embarrassed:
The terms for exams were that if the formulae were engraved on the rule, it was legal to use the rule. Handwritten, slap wrist time (or being thrown out of the exam).
The moral was in those golden days, do your homework prior to buying one and make certain that it was fully engaved  O0

The other long lost idea was that of practicing approximations for use with the slide rule. How many hours did we spend engaged in this?
Yes, the good old days of honest maths.
Sadly practices that are now long since distant memories to most and a foreign concept to modern students. Some of my students wanted to try using both a slide rule and log tables (they had heard of them). Found the little B's using a calculator to add and subtract the log values!
They couldn't even use a calculator beyond (and I quote) Addies up, takies aways, timeses and shares. And these were GOOD class students  :'(
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #17 on: August 27, 2008, 05:35:22 pm »

Quote
A Slide Rule, if it is any good, WILL be made of metal !!!.
Never seen a plastic one, but used lots of METAL ones.

I was rather intrigued by JayDee's earlier post.  I have seen loads of wooden slide rules with plastic? scales, some held on with very small brass pins. (I suspect that some of the early very good quality ones may have even been ivory)?  We all used Faber Castell plastic ones at school - they were approved for use in class.  But contrary to JayDee's experience, I don't ever remember seeing a metal slide rule?

Can anybody offer any input?

Malc
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sweeper

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Re: Can someone teach me to use a slide rule please?
« Reply #18 on: August 27, 2008, 05:49:54 pm »

The Otis King tubular one that I have is metal - at least it has a very heavy metal hand grip, a metal sliding cursor and a very substantial knurled metal top on it. I've never been tempted to try lifting the scales off to check the remainder but going by the weight it surely feels metal.
Certainly "conventional" types, wood, plastic or ivory only.
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Bee

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Re: Can someone teach me to use a slide rule please?
« Reply #19 on: August 27, 2008, 09:25:26 pm »

So when did slide rules drop out of the school curriculum? Around '74 I recon as the Sinclair cheap 4 function calculator came in.
And I presume log tables followed soon after. At university most physicists had memorised enough of the log tables for the rough calculations we did in turorials. I guess nowadays they all reach for their laptops.

Does anyone remember the Curta hand held mechanical adding machine?

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Jonty

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Re: Can someone teach me to use a slide rule please?
« Reply #20 on: August 27, 2008, 09:53:23 pm »

  Seem to remember rally navigators using circular calculators. Was the Curta that thing that looked like a manual coffee grinder?
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #21 on: August 27, 2008, 10:42:24 pm »



Quote
At university most physicists had memorised enough of the log tables for the rough calculations we did in tutorials

I went to technical college with a guy who had memorised 6 figure log/antilog tables - and most of the other tables in that 'little red book'.  He had 50 odd GCE 'O' levels, allegedly including one in Zulu!  He had also completed ALL of the courses that the college offered.

He wore bottle-bottom specs, and a gabardine Macintosh winter and summer.  I guess he must have been the eternal student, effectively unemployable?  I often wonder what happened to him?

Malc



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Re: Can someone teach me to use a slide rule please?
« Reply #22 on: August 27, 2008, 10:50:16 pm »

He's on here Malc. B.P.  ;)
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Re: Can someone teach me to use a slide rule please?
« Reply #23 on: August 27, 2008, 11:58:00 pm »

Quote
[So when did slide rules drop out of the school curriculum? /quote]

Can't answer for schools, we were never told about such exotic devices (secondary modern = factory fodder).
In the tech college, many craft / technician students stuck with logs through till late seventies mainly for cost grounds. I was still teaching the use of logs until mid-eighties.
Not difficult to explain, early calculators eg Texas Industries SR10 only had basic functions plus squares ,square roots and reciprocals. No memory or trig functions.
My first one was that model, bought in New York for around ninety pounds in 1973. Primative but oh so "advanced".(OK, for advanced read novel).
By the time I finished work, the average class had much more calculating power than NASA used for the moon shots. Did it help?
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Reade Models

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Re: Can someone teach me to use a slide rule please?
« Reply #24 on: August 28, 2008, 12:22:56 am »



Hi DickyD

It can't be the same bloke - you....Nah! I can't say that.  {-) {-)

Malc



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