How a Slide Rule works - basic.

Fordman

Fordman

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From the Froggy Chat Memories thread, for those that don't remember how a slide rule worked, here is some very basic explanation.

Slide Rule 01_red.jpg

Aristo Studio slide rule 1966 vintage. They were made with various special features - this model was for Engineering students, note log scales top & bottom, kW/HP conversion. Scales C & D are base value "x", scales A & B are "x squared" (note RH end of scale), scale K is "x cubed", just align the main cursor (on sliding part) and get direct readings. You insert decimal value as required, eg, 3.5/35.0/350.0 all the same on slide rule.


Slide Rule 02_red.jpg

Slide rule set to multiply by 2.0. Scale B = 2 is aligned to Scale A = 1. Everything on scale B is now scale A value x 2.
Example on sliding cursor (kW line) is 3.35 x 2 = 6.70. With practice, 3 decimal places is pretty accurate.
Explanation: The scales are logarithmic, you are adding 2 logarithmic values in this example.


Slide Rule 03_red.jpg

Special feature of this engineering slide rule is kW to HP conversion.
Constant direct reading kW to HP on scales A & B. Note kW line and HP line on sliding cursor. This example set to 0.746 kW = 1.0 HP.
Interesting, as you slide the cursor block left/right the conversion kW/HP is constant. The distance between the 2 cursor lines multiplies by 1.34 so on the logarithmic A scale (or B scale) its a direct conversion.

Takes a bit of practice to use properly, but can handle complex calculations in the right hands. I've pretty well forgotten other than the basics.

Cheers.
 
If you realise you are adding or subtracting logarithms, ie multiply or divide) when the slide is moved, it all becomes simple. At least on the mainscales.
 
Slide Rule 04_red.jpg

A clearer view of the RH end of scales. (Could not edit original post - time expired)
Note direct cross reading of X, X squared and X cubed scales - very quick and handy at the time.
 
I had one when I started but by the end a HP15C, still have it! Not a match to the modern ones which map complex maths which mine does not, I have to do it from first principles. Which can do anything! Even Eulers rules!
 
Matthew said:
I had one when I started but by the end a HP15C, still have it! Not a match to the modern ones which map complex maths which mine does not, I have to do it from first principles. Which can do anything! Even Eulers rules!
Click to expand...
Had a few mates that went to university, they all had the HP calculators with inverse notation that then cost a small fortune.

I was just an apprentice and had a $15 scientific calculator to do my calculations on.

My dad has a slide rule that he used when he was an apprentice, as far as I know he still has it. He did give me a lesson many years ago on how to drive it. Seemed pretty handy for the day and of course the batteries never went flat.
 
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seasink said:
Mine's the top model of these. Quite expensive then. It is made of wood with a plastic "ivory" veneer. a museum piece really.
Click to expand...
I marvel at the mass production of such finely engraved and accurate lines on the scales of these, especially the earlier ones as per your link, but even on the later plastic type which I have, and that it still slides smoothly - I remember using talc powder on the slides I think, and keeping it clean probably helped.
 
These are all twelve inch straight models. Put away somewhere I have a 12 inch diameter circular rule. That's a three feet rule, which allows finer divisions.

The wooden one can stick if it is left too long. If you lube it with a tiny bit of wax where it binds it works again, but too much and it's useless. It bends to release the inner slide when squeezed and grips it again when you let go.
 
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Indeed!

The main scales are logs to base 10. Mine also has LL 1, 2, and 3 scales, which enables natural base e logs and exponentials. I haven't used those for a while!

slide-rule-mania.blogspot.com

Natural Logs with the LL Scales

Okay, we're really going to up the amperage now by switching over to a more endowed engineering type slide rule that'll make short work of n...
slide-rule-mania.blogspot.com slide-rule-mania.blogspot.com

EDIT: The blog says bamboo scales never stick if you use them. It is true.
 
Wow, I have never before looked into the history of slide rules, but it is fascinating.

Just found this in reference to my own slide rule, which is way down the list of Aristo, ARISTO-STUDIO model 0968, mine was purchased Jan 1966. Manufactured in Germany, I have a higher appreciation of it now.
From an international Slide Rule Museum database:
"Aristo was a slide rule manufacturer since 1872. Dennert & Pape was founded by Johann Dennert & Martin Pape, in Hamburg, Germany, and continued under that name until 1936. D&P were the first to laminate and engrave celluloid on boxwood wood slide rules in 1886. Mahogany was used after 1888 and in 1902 started producing slide rules using the System Rietz scales designed by Max Rietz. In 1924 D&P introduced the System Darmstadt slide rule, based on the scales set designed by Prof. Dr. Alwin Walther and began using "DUPA" as a trademark from 1924 to 1936. However, in 1925, the brand became better known as "Aristo", which appeared on slide rules along with "D&P". By 1936 "Aristo" became te official trademark on all their plastic slide rules. The plastic slide rules used Astrolon for the stock and Plexiglas for the cursor. The D&P company name officially became Aristo in 1948 when they introduced all-plastic Duplex slide rules and discontinued mahogany wood models. Aristo stayed in the slide rule business until the end of 1978, a run of 106 years. Aristo was one of the most important slide rule manufacturers world wide."
The Aristo section:

The full museum:

Quite amazing.
 
I bought a comingled box of stuff including 1/2 a dozen circular ones @ a Defence Auction disposal sale [ex Air Force] in the late 60's. Ended up in the rubbish as no one wanted. Then the scientific calculators [high priced then] came on the scene.
 
Fordman said:
Wow, I have never before looked into the history of slide rules, but it is fascinating.

Just found this in reference to my own slide rule, which is way down the list of Aristo, ARISTO-STUDIO model 0968, mine was purchased Jan 1966. Manufactured in Germany, I have a higher appreciation of it now.
From an international Slide Rule Museum database:
"Aristo was a slide rule manufacturer since 1872. Dennert & Pape was founded by Johann Dennert & Martin Pape, in Hamburg, Germany, and continued under that name until 1936. D&P were the first to laminate and engrave celluloid on boxwood wood slide rules in 1886. Mahogany was used after 1888 and in 1902 started producing slide rules using the System Rietz scales designed by Max Rietz. In 1924 D&P introduced the System Darmstadt slide rule, based on the scales set designed by Prof. Dr. Alwin Walther and began using "DUPA" as a trademark from 1924 to 1936. However, in 1925, the brand became better known as "Aristo", which appeared on slide rules along with "D&P". By 1936 "Aristo" became te official trademark on all their plastic slide rules. The plastic slide rules used Astrolon for the stock and Plexiglas for the cursor. The D&P company name officially became Aristo in 1948 when they introduced all-plastic Duplex slide rules and discontinued mahogany wood models. Aristo stayed in the slide rule business until the end of 1978, a run of 106 years. Aristo was one of the most important slide rule manufacturers world wide."
The Aristo section:

The full museum:

Quite amazing.
Click to expand...
1978 would be about the time that calculators were affordable and taking over the slide rules. 1978 would be when I bought my first calculator.
 
As an apprentice early '60s I sometimes had to take the fitters timesheets to the steelworks pay office, after the foreman changed some of the figures ?? My mate worked in there so I was happy to do so and might dally a bit there sometimes. :oops:
They had some big circular slide rules on a mobile stand on wheels that were used for 'complex calculations" I was told. I had a demo once but I did not really know what they were doing. My mate was not at that pay level. The circular scales were used for more accuracy, I understood that OK.
Then later when i did Engineering I purchased a slide rule and used it for some years till $10 calculators took over.
Jaahn
 
In 1974, everyone in Year 6 in NSW was given a circular slide rule. I had mine until about 1990. I kept it in the car, in order to quickly convert litres and km into mpg, by lining up 2.84. I wish I still had it.

Imagine if you pulled out a calculator at the lights today?
 
My father carried a slide rule in his bag until his death. He died only 10 years ago. i still keep it in his bag, it's a 15 cm Castell Reitz 167/87.

I bought a scientific calculator (Sharp EL5000) in 1977 and still use it if I need to do serious calculations.

Roger
 
Roger, I think the shorter slide rules like your father's became more popular in that decade before calculators took over. I remember quite a few people I knew had them, at least they would fit in a pocket within reason.
 
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