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Old 11th Mar 2019, 11:04 am   #41
Herald1360
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Default Re: The slide rule

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Originally Posted by barrymagrec View Post
Is that a wind-up?
Yes unless you're subtracting.

And it probably has a little bell that goes "ting" when you're doing long division (strictly speaking, when you've gone too far and need to undo the last subtraction).

I met a really ingenious one once that did an automatic reverse and carriage shift for division- you just kept on turning the handle anticlockwise. The mechanics must have been one of those "ingenious mechanisms".
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Old 11th Mar 2019, 11:19 am   #42
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Default Re: The slide rule

We had something similar to that at school in the maths room. We were not allowed to touch it. Someone touched it and something fell off it and we got shouted at. That's as far as I ever got with proper mechanical calculators
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Old 11th Mar 2019, 12:10 pm   #43
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Default Re: The slide rule

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And it probably has a little bell that goes "ting" when you're doing long division (strictly speaking, when you've gone too far and need to undo the last subtraction).
Yes, it goes "ting" as you pass through zero, either from positive to negative or vice versa.
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Old 11th Mar 2019, 12:27 pm   #44
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Default Re: The slide rule

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Originally Posted by jez_145 View Post
I left school in 1977 and I think I was probably in one of the last generations to be taught how to use a slide rule. The Maths teacher... ...would produce a giant slide rule, probably 5 or 6 foot long
The top stream maths teacher had one of those fixed to the wall in his room. For the streams below log tables were the pinnacle and in my stream if we needed to count to twenty we took off our shoes and socks.
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Old 11th Mar 2019, 12:54 pm   #45
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Default Re: The slide rule

Anyone remember those mechanical pocket calcuators that you operated with a stylus? They were about the size of a modern calculator and had columns of ratchet-type things that you dragged down with the stylus. The answer appeared in a row of small windows.
These things were all the rage at the Grammar school I went to.
I've found a picture of something similar, but I think the one available in the shops around here was even cheaper and tinny.
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Old 11th Mar 2019, 1:56 pm   #46
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Default Re: The slide rule

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I was taught, rightly or wrong, that with the calculations I had to do was at least know what the ‘ ball park’ would be and if I expected say 0.7 and my answer was 768.9 to think very carefully about does it seem reasonable.
Rightly!

Electronic calculators are brilliant, and for most purposes, the errors introduced are negligible. However, ball-park answers need to be estimated, so you know roughly what to expect, maybe you mis-entered the date, or maybe re-write the expression if it is ill-conditioned.

An example is, n + 1 - n which is obviously 1 , but my calculator gives 0 if n is greater than 10^12.

Richard Feynmann claimed to be able to calculate, within 10 minutes, to an accuracy of 10 percent, any calculation that someone could dictate in under 10 seconds using just pencil and paper. Until one of his University people , on being told, with hardly any hesitation, asked for the tan of pi to the hundredth.

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Would I go back to using a slide rule ? - no way !
Neither would I. In fact, I rarely used mine - log tables are more accurate. But when I bought my calculator (earlier post), the tables were dumped too!
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Old 11th Mar 2019, 2:26 pm   #47
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Default Re: The slide rule

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Anyone remember those mechanical pocket calcuators that you operated with a stylus?
I once saw a couple of interesting ones on Ebay (this was over 10 years ago). One worked in octal, the other in hex. Alas they both sold for way more than I was prepared to pay (I think getting on for £500 each).

On the other hand I spotted one in a charity shop a few years ago that worked in pounds/shillings/pence. That was a much more reasonable price so I bought it.
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Old 11th Mar 2019, 2:30 pm   #48
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Default Re: The slide rule

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Originally Posted by kalee20 View Post

Electronic calculators are brilliant, and for most purposes, the errors introduced are negligible. However, ball-park answers need to be estimated, so you know roughly what to expect, maybe you mis-entered the date, or maybe re-write the expression if it is ill-conditioned.

An example is, n + 1 - n which is obviously 1 , but my calculator gives 0 if n is greater than 10^12.
The HP15C had an (optional?) advanced user manual that had a chapter on why the calculator sometimes gave the wrong answer. It covered things like rounding errors.

But that was when products came with useful documentation.

I feel that now 'everybody' uses an electronic calculator, spreadsheet, or other similar aid that rounding errors and the like should be taught in schools. If you're going to use a machine you need to know how to use it correctly.
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Old 11th Mar 2019, 2:38 pm   #49
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Default Re: The slide rule

Somewhere I must still have my British Thornton double-sided slide rule which dates from 1970.

This was just before mass-market electronic calculators when we used slide rules every day at school along with our trusty log and trig tables - happier and simpler times!
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Old 11th Mar 2019, 2:46 pm   #50
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Default Re: The slide rule

We got a HP35 at work by getting HP to invoice it as "HP35 integrated circuit module": we were purchasing and designing various expensive ICs at the time on a MOD project, and it was a way of sneaking the purchase order past the accountants. AFAIR it cost around £220!

I still have my Thornton Pic ( with the log log scales that we needed for one college module, but I can't recall which one), and my school "Nutalls" log tables. I think I have used the log tables more recently than the slide rule, when I needed the tangents table.

Interesting re-reading some of my old science fiction books where the "calculators" are people who use "slip-sticks". I never heard them called that in the lab, they were "guessing sticks".

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Old 11th Mar 2019, 3:10 pm   #51
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Default Re: The slide rule

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Anyone remember those mechanical pocket calcuators that you operated with a stylus?
Yes, I used to own one. In fact, my sister claims that she still has it somewhere, but can't find it - so I may yet be able to unite with the rest of my collection.

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Originally Posted by TonyDuell View Post
One worked in octal, the other in hex.
I used to have a scientific (electronic) calculator that had an option of hexadecimal.
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Old 11th Mar 2019, 4:03 pm   #52
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Default Re: The slide rule

I sat my maths O-level in 1986 (a year early; did Additional Maths AO-level in '87, A-level in '88 and A-level Further Maths in 1989. All worth it to get out of PE!) We used 3-figure log tables, but I already knew how to use 4-figure tables anyway, and were entered for the "non-calculator" exam.

My Grandad on my Dad's side of the family was an engineer, and when he passed away I inherited the newer of his two slide rules. It's a 25cm. plastic one, made in Japan by Jakar and probably one of the last slide rules ever made (early to mid 1970s by my reckoning).

I can use it (need to refer to the instruction manual occasionally for the trig and log-log scales), and still get it out sometimes if I need a quick product or ratio. I was thinking of taking it to work and putting it in a glass case in the server room, with the legend "In case of emergency, break glass" .....

By the way, if anyone still has a copy of Frank Castle's 4-figure Logarithmic and Other Tables for Schools, try multiplying 2 * 2 .....
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Old 11th Mar 2019, 4:28 pm   #53
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Default Re: The slide rule

Julie, that sounds like me, only ten years earlier!

I had a casio fx-31 around that time (with the VFD). But I also had a WH Smith slide rule which was described as a 'modified Weiss' whatever that means. As someone pointed out, the slide rule was good for finding a close resistor ratio, something that would take an age to do with a calculator. I also owned an early CBM calculator which, unusually, used a 9V battery.
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Old 11th Mar 2019, 4:33 pm   #54
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I have a 250mm Jackar too 1005 model, nice rule, mine is the engineers version none of the fancy maths stuff on it, single sided and given a following wind will do three digits (which works out as 0.25mm on the scale, more than enough for electronics). Got it from eBay with box, instructions and plastic sleeve for a couple of quid. You are probably right that they are the last made.
 
Old 11th Mar 2019, 4:34 pm   #55
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Default Re: The slide rule

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But I also had a WH Smith slide rule which was described as a 'modified Weiss' whatever that means. .
Not a simplified Reitz?
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Old 11th Mar 2019, 4:51 pm   #56
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Default Re: The slide rule

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By the way, if anyone still has a copy of Frank Castle's 4-figure Logarithmic and Other Tables for Schools, try multiplying 2 * 2 .....
You get 3.999. I know, I tried it years ago. Cumulative rounding errors bite!

But it's still better than slide-rule accuracy which would be difficult to read to better than 'somewhere between 3.99 - 4.01.'
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Old 11th Mar 2019, 4:59 pm   #57
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Default Re: The slide rule

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Not a simplified Reitz?
You're right. My brain cells fail me again
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Old 11th Mar 2019, 5:17 pm   #58
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Default Re: The slide rule

That reminds me that we used to have a Texet calculator that took a 9V PP3 battery. Eventually the segments in the display started to fail. I think ours came from Woolworths.

I remember a lecturer pointing out that slide rules were perfectly adequate for most engineering calculations. The meters we used in the power lab were mostly only accurate to 5%, and in civil engineering you usually multiplied your results by a safety factor of anything up to 10 anyway, so no need for four significant figures accuracy.

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Old 11th Mar 2019, 6:21 pm   #59
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I remember a lecturer pointing out that slide rules were perfectly adequate for most engineering calculations. The meters we used in the power lab were mostly only accurate to 5%, and in civil engineering you usually multiplied your results by a safety factor of anything up to 10 anyway, so no need for four significant figures accuracy.
May have been the case years ago, but not now!

Building in a safety factor of 10 means your product is larger, heavier, and costlier than one where a smaller safety factor is built-in. So a company which can assess its design more accurately will win.

I have often assessed efficiency of switch-mode power supplies. If I measure input volts to an accuracy of 5%, input current to 5%, output volts to 5% and output current to 5% and then calculate powers using a slide rule to 1% I get an uncertainty in input power of 11%, an uncertainty in output power of 11%.

So my input of 100W and output of 85W (15W losses) could actually be input 111W and output 75.6W. That's 35W of losses! More than double the nominal! So to be safe, instead of one quiet fan I'm going to have to be safe and specify two, noisier ones. My competitor, with accurate meters and a calculator, will be laughing all the way to the bank!
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Old 11th Mar 2019, 6:26 pm   #60
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Default Re: The slide rule

A friend of mine at university had an HP35 calculator not long after they came out but wasn't allowed to use it in exams. We reckoned that not only could he make more accurate mistakes than the rest of us but he could make them faster.

When I started work the company introduced a scheme where we could buy a Commodore calculator through the company and pay for it over a few months. I managed to get one of the second batch they bought in but needed a plug for the charger so I went to the stores but they couldn't just give me a plug so it went down as a plug for a power supply without specifying exactly what the power supply was. I've still got the calculator but the nicads died many years ago, however it still runs from the charger.

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