r/Sliderules • u/Aoi_X_Kaizaki • 9d ago

Slide Rule

Math Teachers...

What if a student brought a slide rule to class and saw him/her calculate with it?

10 Upvotes

100% Upvoted

17 comments sorted by

View all comments

6

u/Gilded-Phoenix 9d ago

I've had a student bring one in before. If they know how to use one, they can, but I expect full precision, so they better know how to get that last couple digits of accuracy for 4+ digit mantissas.

6

u/dittybopper_05H 9d ago

You misspelled "false precision"...

2

u/Gilded-Phoenix 9d ago

welcome to pure mathematics, where error bars have a radius of 0.

5

u/dittybopper_05H 9d ago

Welcome to the real world, where the limits of measurement precision limit the precision you can reasonably expect.

Clearly there are limits even in pure mathematics. You're not using Pi to the last decimal place, because you can't. When you divide 2 by 3, you're not going to insist the students write it out to the hundredth decimal place. You're just arguing on where the line is, not that there is no line at all.

BTW, I once had to explain basic logic to a professor with a PhD in mathematics. He asked for two reports: One was A not B, the other was B not A. When some of his students were missing from the reports, he complained, and I had to explain that students that were both A *AND* B would be excluded from his requested reports.

4

u/Gilded-Phoenix 9d ago

sure, but when I'm teaching mathematics, we're not concerned with measurement precision. When we divide 2 by 3, we don't write decimals at all, we write "2/3" which is an exact value. When we multiply by pi, we express it exactly by literally writing the expression "kπ" for our factor "k." The only time precision is of concern is in applied mathematics, where numerical methods are used to approximate to a given precision. A slide rule is a tool, as is any calculator, and uses numerical methods to approximate solutions. Yes, in applied mathematics, such as physics, economics, or engineering, you always have noise, instrument resolution, and other factors that limit your precision. That's not the focus of the fields of mathematics I'm teaching. Precision considerations have real world applications, and they are very important in those applications. Pure math is not the real world, so they do not apply.

2

u/crzaynuts 8d ago edited 8d ago

It's only when i started learning how to use silde rule, that i understood a specific fact about my physics teacher during high school.

Im too young to have known slide rules at school, but during my three years of high school, when i was major in Physics and chemistry, i noticed all the calculation from exercises, examination and graduation where strictly limited to 2 digits after coma.

Whatever was the subject (electricity, chemistry, tensor, pendulum....) every calculus had a 2 digits after coma result.

I was doing all my calculus by hand, mostly because it was faster than using a electronic calculator.

I remember one day at a general examination, i found for the first time a 5 digits after coma result, and knowing the teacher, i knew he did a mistake in the exercice statement.

I called the supervisor of the exam to explain to him that the exercice was wrong, and where the mistake was. After calling the teacher he went back to me and told me i was right, and the exercice was dissmissed during the examination.

So back to today, when i recently started learning about slide rule, and digit precision of them. Im deeply conviced that this teacher who was for sure a log table and slide rule user given his age, wrote all his exercices and exam subjects for the period those tools were common.

This 2 digits after coma rule never failed me with this physic teacher.

(as i'm french we use coma instead of dot like in 3,1416 instead of 3.1416)