I got a kick out of reading this retrospective of Texas high school slide rule competitions… including a 1959 picture of Janis Joplin on her high school slide rule team and a 1980 Dallas Morning News article eulogizing the competition.

## All posts tagged **slide rule**

# Texas slide rule competitions

*Posted by John Quintanilla on March 4, 2019*

https://meangreenmath.com/2019/03/04/texas-slide-rule-competitions/

# Slide rule

To give my students a little appreciation for their elders, I’ll demonstrate for them how to use a slide rule. Though I have my own slide rule which I can pass around the classroom, demonstrating how to use a slide rule is a little cumbersome since they don’t have their own slide rules to use.

I recently found an applet to make this demonstration a whole lot easier: https://code.google.com/p/java-slide-rule/

*Posted by John Quintanilla on February 3, 2016*

https://meangreenmath.com/2016/02/03/slide-rule/

# Square roots and logarithms without a calculator (Part 7)

I’m in the middle of a series of posts concerning the elementary operation of computing a square root. This is such an elementary operation because nearly every calculator has a button, and so students today are accustomed to quickly getting an answer without giving much thought to (1) what the answer means or (2) what magic the calculator uses to find square roots. I like to show my future secondary teachers a brief history on this topic… partially to deepen their knowledge about what they likely think is a simple concept, but also to give them a little appreciation for their elders.

Today’s topic — slide rules — not only applies to square roots but also multiplication, division, and raising numbers to any exponent (not just to the power). To begin, let’s again go back to a time before the advent of pocket calculators… say, the 1950s.

Nearly all STEM professionals were once proficient in the use of slide rules. I never learned how to use one as a student. As a college professor, I bought a fairly inexpensive one from Slide Rule Universe. If you’ve never seen a slide rule, here’s a picture of a fairly advanced one. There are multiple rows of numbers and a sliding plastic piece that has a thin vertical line, allowing direct correspondence from one row of numbers to another. (The middle rows are on a piece that slides back and forth; this is necessary for doing multiplication and division with a slide rule.)

Let’s repeat the problem from Part 6 and try to find

.

We recall that . The logarithm on the right-hand side can be estimated by looking at a slide rule. Here’s a picture from my slide rule:

The important parts of this picture are the bottom two rows. Note that the thin red line is lined up between and ; indeed, the red line is about one-third of way from to . On the bottom row, the thin red line is lined up with . So we estimate that , so that .

Working the other direction, we must find . We move the thin red line to a different part of the slide rule:

This time, the thin red line is lined up with on the bottom row. On the row above, the red line is lined up almost exactly on , but perhaps a little to the left of . So we estimate that or .

The correct answer is .

Not bad for a piece of plastic.

Because taking square roots is so important, many slide rules have lines that simulate a square-root function… without the intermediate step of taking logarithms. Let’s consider again at the above picture, but this time let’s look at the second row from the top. Notice that the thin red line goes between and on the second line. (FYI, the line repeats itself to the left, so that the user can tell the difference between and .) Then looking down to the second line from the bottom, we see that the square root is a little less than , as before.

In addition to square roots, my personal slide rule has lines for cube roots, sines, cosines, and tangents. In the past, more expensive slide rules had additional lines for the values of other mathematical functions.

More thoughts on slide rules:

1. Slide rules can be used for multiplication and division; the Slide Rule University website also a good explanation for how this works.

2. In a fairly modern film, Apollo 13 (released in 1995 but set in 1970), engineers using slide rules were shown to dramatic effect.

3. Slide rule apps can be downloaded onto both iPhones and Android smartphones; here’s the one that I use. I personally take great anachronistic pleasure in using a slide rule app on my smartphone.

4. While slide rules have been supplanted by scientific calculators, I do believe that slide rules still have modern pedagogical value. I’ve had many friends tell me that, when they were in school, they can to construct their own slide rules from scratch (though not as detailed as professional slide rules). I think this would be a reasonable exploration activity that can still engage today’s students (as well as give them some appreciation for their elders).

*Posted by John Quintanilla on August 7, 2013*

https://meangreenmath.com/2013/08/07/square-roots-without-a-calculator-part-7/

# Advertising for slide rules, from 1940

I’m about to begin a series of posts concerning how previous generations did complex mathematical calculations without the aid of scientific calculators.

Courtesy of Slide Rule Universe, here’s an advertisement for slide rules from 1940. This is a favorite engagement activity of mine when teaching precalculus (as an application of logarithms) as well as my capstone class for future high school math teachers. I have shown this to hundreds of college students over the years (usually reading out loud the advertising through page 5 and then skimming through the remaining pictures), and this always gets a great laugh. Enjoy.

test

*Posted by John Quintanilla on July 31, 2013*

https://meangreenmath.com/2013/07/31/advertising-for-slide-rules-from-1940/

## Top Posts & Pages

- Derivative of 1/x
- Was There a Pi Day on 3/14/1592?
- Engaging students: Finding the domain and range of a function
- Engaging students: Graphing an ellipse
- Full lesson plan: magic squares
- Cow-culus
- Engaging students: Congruence
- Engaging students: Factoring quadratic polynomials
- Square roots and logarithms without a calculator (Part 3)
- Exponential growth and decay (Part 3): Paying off credit-card debt

## Archives

- March 2019
- February 2019
- January 2019
- December 2018
- November 2018
- October 2018
- September 2018
- August 2018
- July 2018
- June 2018
- May 2018
- April 2018
- March 2018
- February 2018
- January 2018
- December 2017
- November 2017
- October 2017
- September 2017
- August 2017
- July 2017
- June 2017
- May 2017
- April 2017
- March 2017
- February 2017
- January 2017
- December 2016
- November 2016
- October 2016
- September 2016
- August 2016
- July 2016
- June 2016
- May 2016
- April 2016
- March 2016
- February 2016
- January 2016
- December 2015
- November 2015
- October 2015
- September 2015
- August 2015
- July 2015
- June 2015
- May 2015
- April 2015
- March 2015
- February 2015
- January 2015
- December 2014
- November 2014
- October 2014
- September 2014
- August 2014
- July 2014
- June 2014
- May 2014
- April 2014
- March 2014
- February 2014
- January 2014
- December 2013
- November 2013
- October 2013
- September 2013
- August 2013
- July 2013
- June 2013

## Categories

- Algebra I (171)
- Algebra II (275)
- Bases (43)
- Calculus (227)
- Chemistry (9)
- Computer science (9)
- Discrete mathematics (217)
- Elementary (149)
- Engagement (676)
- Geometry (209)
- Guest presenter (402)
- History (54)
- Humor (240)
- News Clips (119)
- Physics (35)
- Popular Culture (215)
- Pre-Algebra (153)
- Precalculus (492)
- Preparing for college (12)
- Probability (82)
- Statistics (78)
- Tales from the Classroom (211)
- Technology (76)
- Theorems (152)
- Uncategorized (57)

## Tags

angle arccosine arcsine arctangent area bag of tricks binary circle combinatorics Common Core complex numbers compound interest conceptual barrier confidence interval convex polygons cosine decimal De Moivre's Theorem derivative differential equation distributive law divisibility division algorithm e exponent exponential factorial factoring fraction function gamma geometric series graph high-stakes testing hypothesis test index to a series of posts induction integral inverse function law of cosines law of sines limit logarithm logic MAA magic trick matrices multiplication Pascal's triangle perpendicular pi polar coordinates polynomial primes PRIMUS proof Pythagorean theorem Pythagorean trig identities quadratic formula residue sequence series sine slope sports square root system of equations tangent Taylor series textbook problems triangle trigonometry unsolved problems volume xkcd## Meta