The Big Slide Thread

[kvom]

I used slide rules all through university in the late '60s. I had a bad habit of losing them periodically, which became expensive. I created a geocache years later that required knowledge of a slide rule and logarithms to calculate the GPS coords:

https://www.geocaching.com/geocache/GCRFRB

 

[Gordon]

I used a slide rule frequently in one of my first jobs. It was a sales office where we purchase the parts and subcontracted fabrication of special equipment that we, the engineering department designed. At the end of the job we had to recap the job to determine how much the engineering department had earned or lost on each job. That involved calculating a 15% markup on all purchased parts and labor. That was done by dividing the cost by 85 which was done with a slide rule. The accounting department was always trying to transfer engineering department funds to other department. This was in the days before everyone had a calculator. The only calculator was a mechanical Monroe on the accounts desk thus the slide rule calculations. We usually came out within 1% of the accounting department because the estimates on the precision of the slide rule were as often high as they were low so in the end it came pretty close.

On a side note: There was always an uneasy relationship between the accountant and the engineering department. Periodically when he went to the restroom someone would go up to his desk and divide some number by zero and the that would cause an endless loop and the mechanical calculator would just keep clunking away until someone stopped it or the bearings gave out.

 

[stanstocker]

I had to look that one up.
Found a picture below.

And they forced us to use a Smith Chart in the field theory class.
I must confess, I never got the feel for using a Smith chart.
I understood that it was a tool used to solve fields problems, but it also has sort of a corn maize feel to it too.
I have seen others use a Smith chart, such as my profesor, and so I know it works.
The first thing that came to mind when I saw a Smith chart was "what the flock are they trying to make use do now?".
Sort of like Chinese water torture; the things they use to force us to use.

.

It had been many years since plotting my last Smith Chart. Recently I bought one of the two port 3 GHz VNA gizmos that are now less than $200 USD for playing with some antenna and feedline designs, an old interest that I have time to fool around with now. It's quite interesting how useful a Smith chart is when a gadget plots it for you, all the impedance vectors plotted in seconds with that lovely 50 ohm point dead center.

Hopefully re-learning some of this stuff and keeping on learning new things will help keep the aging brain from turning to mush.

As asked in the fine film Airplane, "What's the vector Victor?

 

[L98fiero]

Ironically, this is sort of what I consider the "slide rule" of lathes; ie: it is old, manually operated, clunky compared with modern CNC machines, but a very capable machine in the hands of someone who knows how to use it.
The new guys would say "Where is the keyboard ?".
.

The first shop I worked in had a number of lathes like that with added on electric motors and a four speed transmission, one of them had a 6 foot swing spindle and a 2 foot swing on the same lathe. The story was that the shop had a foundry at one point and when the city streetcar barns burned, they were given that lathe that was used to recondition the wheels as scrap, they got a job that requires a large swing so the bronze bearings were replaced and it was put back into use. It wasn't used often but it was the only lathe that size anywhere close.

 

[a41capt]

It had been many years since plotting my last Smith Chart. Recently I bought one of the two port 3 GHz VNA gizmos that are now less than $200 USD for playing with some antenna and feedline designs, an old interest that I have time to fool around with now. It's quite interesting how useful a Smith chart is when a gadget plots it for you, all the impedance vectors plotted in seconds with that lovely 50 ohm point dead center.

Hopefully re-learning some of this stuff and keeping on learning new things will help keep the aging brain from turning to mush.

As asked in the fine film Airplane, "What's the vector Victor?

I purchased a NanoVNA for my antenna experiments, and can’t believe how powerful something that small can be, and all for $50 American!

John W

 

[Richard Hed]

I was fascinated by slide-rules and learned how to use one, and then used it exclusively for a Physics I, and Chemistry course in college. (I'm a 90s kid) It turns out, that the types of problems you have to solve there lend themselves very well to the slide rule.

To use one, you have to understand that log(A*B) = log(A) + log(B), and also understand that the calculations across powers of ten result in the same digits. i.e. 25 * 4 = 100, but also 0.25 * 0.4 = 0.100 Same digits, but the decimal place moves. Tracking the decimal place (in your head) as you continue calculations is the toughest part, but it isn't really that difficult.

Since the "rule" of the slide rule is laid out logarithimically, (i.e. the lines get closer together the closer you get to the right), when you add together the distance from the edge of the outer to the edge of the inner, you are actually adding together log(A) and Log(B). So multiplication is done just by "adding" the two distances together, i.e. looking to see what number across from B on the A scale.

Physics & Chemistry are a bunch of calculations that are a string of multiplication and division. And because A*B/(C*D) = A/B * C/D freely, you can just accumulate the end result by adding and subtracting on the slide rule, while keeping a running total of what decimal places you are adding on/off.

The slide rule is one of the reasons that "scientific notation" is a thing. As you write a number in scientific notation, you are effectively preparing it *directly* for being applied to the slide rule. You see immediately the whole+partial number that is the distance you are going to slide on the rule, and you see directly the powers of ten that you are tracking during the calculation.

Further, because of the limitations of precision (you can only slide the rule so precisely. Maybe you can enter 1.27, but not 1.275); the slide rule naturally maintains significant digits for you. You don't have to wonder if you have bonkers unrealistic precision in your result. (A simple example: 1 / 3 = 0.3333333333333 on a calculator, but there is no way you could guarantee OR measure that accurately). The slide rule will never give you a result like that beyond your significant digits.

It is actually a beautiful instrument, but I admit it has its niche in real-world applications like physics and chemistry, and not more abstract subjects like maths.

I understand that one of the reasons calculators added significant digits is that in constructing the Interstates, after calculators became available, is that the first calculators had 8 digits, but then the interstates at curves and bridges started to be off a foot or two after miles of laying concrete. It turned out sine and cosine needed more accuracy so they developed 10 place calculators. In physics, one might need 10 places (or even more), particularly in astronomy. I can use slide rules and if I see one at a garage sale, I certainly will grab it up.

 

[Richard Hed]

This first slide rule I used on first model aircraft engines I designed back 1960's . This slide ruler was designed for drafting tables. On the backside has cork at each end and center has units like miles to k meters and N miles .
Meter conversion to English.

Work great till electronic calculators cameout.

It handy for some I could do log for formula like navigation calculations like great circle navigation.

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Dave

I'll buy it. HOw much?

 

[Gordon]

I do find it interesting that folks are upset about the "Break Room" category going off topic. I have never even noticed that there was such a category. I always just load unread topics which includes all topics and then I read the ones that I am interested in and mark all topics read so everything shown is new. If I am interested in a particular topic I may follow that topic which gives me an email alert.

 

[Richard Hed]

I do find it interesting that folks are upset about the "Break Room" category going off topic. I have never even noticed that there was such a category. I always just load unread topics which includes all topics and then I read the ones that I am interested in and mark all topics read so everything shown is new. If I am interested in a particular topic I may follow that topic which gives me an email alert.

Precisely. I don't get it either.

 

[HMEL]

did you ever master the slide rule or did anyone ever master it, I go one last week at an estate sale with a bunch of machinist tools and the Kennedy toolbox, I would like to find instruction on the slide rule to see what it is all about, Joe

There are several older text books that describe how to use a slide rule. It is based on logarithms and so when you move the slides you simply are adding the logs of numbers and are multiplying and dividing. A good rule will have several scales to use. The challenging part of using one is maintaining in your head where the decimal point is in the number and the specific digits that are meaningful in the answer.

I once asked a professor what the difference in teaching with modern calculators vs a slide rule was and he replied I can now ask questions without the thought of how difficult the math might be. Sort of a good news bad news if you are a student. A question requiring a calculator is likely to be more complex and involved.

Another fun fact is the materials used to make them were designed not to expand with and contract with temperature. Thats to maintain accuracy in the scales. They can be quite expensive and good ones are now hard to find.