Units Matter

Published by patrick honner on

As someone who has long considered himself a “pure math” person, as opposed to more of a “science” person, I never really cared much about the units of expressions; kilograms, meters, Newtons, and the like.  The numbers were all I ever really cared about. Well now I see what can happen when this attitude is taken too far.


It took me about 3 days of driving around Puerto Rico before I realized that speed limits were posted in miles per hour and mile markers were posted in kilometers. Driving around a foreign country (territory?) is challenging enough without having to perform a bunch of conversions in your head.

Just to further complicate matters, plenty of signs left it open to driver interpretation.

velocidad maxima

Categories: Appreciation

patrick honner

Math teacher in Brooklyn, New York


Bon Crowder · March 22, 2011 at 1:19 pm

I, too, am a pure math person. It wasn’t until working with oilfield hands for four years that I really understood the benefits as well as the challenges of units.

Thanks for sharing the pictures!

MrHonner · March 22, 2011 at 10:14 pm

Someone recommended Street Fighting Mathematics to me, and the sophisticated stuff he does with dimensional/unit analysis just blows my mind. It really made me start thinking about taking units more seriously.

These signs in Puerto Rico just offended my common sense. Doesn’t anyone down there think it’s crazy that the speed limit is 55 mph, but the sign that says “Ponce 108” means it’s 108 kilometers away?

Cathy Campbell · March 28, 2011 at 11:45 pm

Very surprising that both units would be used around Puerto Rico at the same time!

Not sure if you would ever need an example of metric/imperial conversion mistakes but I thought I would pass it on, just in case. Have you heard of the Gimli Glider? I don’t want to give it away but this story is about the use of metric and imperial measurements that could have had dire consequences for crew and passengers on a 767 airplane in the 1980s. I have a personal connection to this story because my aunt and her two young children were on this flight. I also am a math teacher and I use this story to emphasize the importants of measurements and appropriate units. Here is the link to the first of five parts: http://www.youtube.com/watch?v=1lBsqEtKTGU

Hope you find it interesting.

MrHonner · March 29, 2011 at 6:47 am

Thanks for the link, Cathy! I look forward to checking out the story.

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