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# Slide Rules vs Scientific Calculators.

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#### schmitt trigger

Not exactly an antique electronics question, but an antique instrument extensively used by REAL engineers in the past.

How many among you actually used a slide rule?

When I was starting engineering college back in the summer of '74, I had serious misgivings about being capable to become an engineer as I had a rough time with the slide rule.
True, Hewlett-Packard had already brought the HP35 scientific calculator, but at close to US$600 which was A LOT OF MONEY at the time, it was too expensive for me. Then Texas Instruments brought out the SR50 for about US$200, which still was expensive, but barely within my reach by working all summer long.

The TI SR50 really saved my engineering career.

Do you have any similar stories of yours?

#### SLK001

##### Full Member level 6
I used a LOG-LOG DUPLEX VECTOR by K&E for quite a while. It was my father's (also an engineer). When the TI-50 came out, he bought one for me for my birthday. I would have purchased an HP35, but I hated the reverse Polish method of entering equations. I now have TI-50 clones that run on a SR-44 battery for years.

The slide rule would do quite a lot, but you had to keep track of the "powers". I usually wrote them on a piece of paper and calculated the final power at the end. The calculators make you lazy and let your math skills atrophy. They said the same thing about slide rules.

#### jiripolivka

I used a LOG-LOG DUPLEX VECTOR by K&E for quite a while. It was my father's (also an engineer). When the TI-50 came out, he bought one for me for my birthday. I would have purchased an HP35, but I hated the reverse Polish method of entering equations. I now have TI-50 clones that run on a SR-44 battery for years.

The slide rule would do quite a lot, but you had to keep track of the "powers". I usually wrote them on a piece of paper and calculated the final power at the end. The calculators make you lazy and let your math skills atrophy. They said the same thing about slide rules.

Like all others old-timers I used the slide rule, and tables of functions and paper calculations, all together. Once I won a contest with a colleague who used a slide rule, I used paper and pencil, in a complex calcuation of third powers and back.

When the HP-35 was available, I borrowed one for many sinh and cosh calculations. It was fast but quite false. The error was bad when I finished my thesis. HP did not include this error in the specifications: sinh and cosh series do not converge well.

Do not trust all the digital stuff was what I learned. Most computers I used were extremely unfriendly including all Windows, the result of poor software (is it the intention?)

#### schmitt trigger

Searching the web, there are many sites documenting the algorithm errors mostly due to truncation.

But when one looks back at the state of the art VLSI design of the early 70s (PMOS only???), it was an amazing engineering feat to have all this computing power on a battery-powered, handheld design.

It was very clever to use lenses to enhance the visibility on the LED display, as LEDs back then were quite inefficient.

#### jiripolivka

Searching the web, there are many sites documenting the algorithm errors mostly due to truncation.

But when one looks back at the state of the art VLSI design of the early 70s (PMOS only???), it was an amazing engineering feat to have all this computing power on a battery-powered, handheld design.

It was very clever to use lenses to enhance the visibility on the LED display, as LEDs back then were quite inefficient.

I agree, everybody was fascinated by the new technology and what all it could do in a tiny case and a small battery. In 1980s I acquired a Casio Fx-115 x scientific calculator, and over 35 years I had used it daily, without any problem.
The slide rule had been in use , however, for more than 100 years, needed no battery, only good handling. The main disadvantage was that it could not sum. Even now it is a good idea to use paper and pencil to check orders, etc.

#### E-design

Well, I still have my **broken link removed** slide rule somewhere. I also have my functional HP 25C from college days.
These days I prefer the HP 50G though.

#### KlausST

##### Super Moderator
Staff member
Hi,

I know the slide rules, but never really used them.
Only a couple of years before they used them in school.

In 1980s I acquired a Casio Fx-115 x scientific calculator, and over 35 years I had used it daily, without any problem.
In the early 80s a bought a CASIO fx-82.
It still is on my desk and used almost every day. And - unbelievable - still the first set of batteries: Blue CASIO AA.

Many of my "raw estimations" are done with head, pencil, paper, construction...

Some bulky calculations I do with Excel, some with good old (quick and dirty) VB6 programs.

Klaus

#### E-design

I also had a Casio fx-15 but that got stolen along the way. I loved its display.

#### andre_luis

##### Super Moderator
Staff member
I'm pretty sure that there had a scene on the "Apollo 13" movie at which one of the characters was calculating something of the re-entry route into the Earth by using a slide rule.

I never had used the slide rule in my professional career, but I had used nomographs once in a while, and it was even taught somewhere in the engineering course how to build a nomograph from a determined formulas; a knowledge increasingly limited to ancients :smile:.

##### Super Moderator
Staff member
I used a slide rule in high school and college. It made a lot of calculations easy. I wish it could have done all calculus functions too because it was a chore to do those repeated calculations of areas under a curve. All I could think was, Why not program a computer to do it? We students had access to an IBM360 at the university. That was when you had to be rich to own one (circa 1970).

##### Super Moderator
Staff member
High school for me was no slide rules, and no HP-67/97s allowed (which nobody but the north side kids could afford) later it was the HP-31/33 and the TIs 59 then the 50 and 35 that weren't allowed. You could only use calculators at home to "check" your answers, because every calculation had to be done by hand and no skipping steps if you wanted any chance of partial credit for the problem if your answer ended up wrong, e.g. due to say a sign error in the last step.

In college I had an HP-41 and used the old IBM360 for a programming class as the newly bought VAX was heavily (over) used and I could never get on it. But since everyone wanted to use the VAX the IBM360 was hardly used at all, it was extremely easy to get your cards run on it any time you wanted . I actually usually handed my programs in days before anyone else in the class, due to not having to wait. That was until others in my class started noticing I was getting my programs done early, then it started getting busier in the IBM360 lab. :-(

#### schmitt trigger

In college we had access first to a CDC-3300 and later an IBM370. Running on punched cards.

What I remember is, that near the end of term the computer would be very busy, so you had to be there well before dawn or on weekends, if you wanted the slightest chance for your program to be compiled.

The other bottleneck was access to the card punchers. On those days of FORTRAN and COBOL, the smallest grammatical mistake, and the compiler would abort the program.
So if one found that had missed a comma, one had to run to the card punchers to correct the error, only to find a long queue of people in the same situation!!!

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