Slide rules

[Adam Funk]

You're right; thanks for the correction.

[Colin Wilson]

more sense now :-}

I suppose it'd help if I knew what the hell the different scales I was supposed to be looking at were !

[Bob Eager]

Use the link at the bottom of the page I quoted, to get 'back' to a page that explains a bit more.

Most basic are the A and B scales; simple scales for multiplication. Slide 1 on B to the multiplicand on A. Then read off the product on A against the multiplier on B (any value you like, so it makes a kind of 'times table').

C and D are similar but only cover one order of magnitude instead of two. This gives better accuracy, but at the expense of 'going off the end' and having to scale things sometimes.

DF and CF (if you have them) work similarly, but run from pi to pi*10, which keeps some calculations in a more convenient pace on the rule.

Other scales (rules vary) have simple read-offs of squares and cubes, log, sin, tan, exp, reciprocals, etc.

[Harry Bloomfield]

Mary Fisher wrote on 03/06/2008 :

I first came across slide rules at college and also found them absolutely fascinating - once you had accepted the idea of not needing absolute precision.

I have never been much good at doing it in my head, I always need to write the figures down to help me 'visualise' it. I suffer a poor short term memory, unless I put in a massive effort to remember figures. I must say I do occasionally ignoring a calculator and working things out on paper just to refresh the way I was taught combined with the self taught short cuts I devised.

[geoff]

Ooh, I had one similar, but in green, circa 1965

[geoff]

[geoff]

Pah - there is only one ...

Kaye and Labey

As for log tables - light blue book with white text on the cover, somewhere

[geoff]

I USED to be able to do it to 30 places

but then, I used to know the correct name for the capital of Thailand too

(Krung Thep Mahanakhon Amon Rattanakosin Mahinthara Ayuthaya Mahadilok Phop Noppharat Ratchathani Burirom Udomratchaniwet Mahasathan Amon Piman Awatan Sathit Sakkathattiya Witsanukam Prasit)

sad, or what ?

[Colin Wilson]

I'm looking at the virtual one at:

I really can't get my head around even the "simple" one - there is no B :-}

[Andrew Gabriel]

Or is that the Thai version of the early 1970's Pepsi advert?

[Bruce]

They are logarithmic scales. You add the logarithm of one number to the logarithm of the other. The sum or the two logarithms is the logarithm of the product of the two numbers.

In other words, log(a) + log(b) = Log (a x b).

For example, log(2) + log(3) = log(6)

The slide rule makes the conversion into logarithms for you. All you have to do is input the two numbers, and read off their product.

[Bob Eager]

I'm not surprised - that is a bit weird. You can add and remove scales, and everything, but...

Here's a nice simple one...!

[Bob Eager]

If you look at the emulator mentioned, you'll see why he's confused!

[geoff]

In message , Andrew Gabriel writes

I learnt it in Thailand in the mid 70's

[The Natural Philosopher]

Sliderules don't do sums. They do multiplicatin and division, and trig and logs.

You are expected to be able to add up before you use one.

[Andy Hall]

[dennis]

If you are going to be pedantic.. they only add or subtract numbers. You are expected to know what the scales mean.

No need, I have seen slide rule price comparators that were simple enough for a granny to work out which pack was cheapest, no sums involved.

[Bruce]

Good grief! How to make a simple task complicated! ;-)

[Bob Eager]

The one I mentioned afterwards is usable with the basic directions I gave...

[Colin Wilson]

Result: still can't get my head around it :-}

I think you were talking about moving the cursor to the value of B on A, once you set the A & B to the values you want to multiply to read the answer.

The first one I tried worked, but nothing beyond that :-}