The Measure of Pearly Whites

Vintage_Dental_FlossBy The Metric Maven

Mini Bulldog Edition

One day when I was visiting my dentist, I took note of a procedure whose details I had ignored for many years. My dental hygienist had me wait a moment while she found a person to help her. In this age of computerized toasters, the assisting woman appeared with a clipboard. I was reclined and expect this woman sat down in a chair located behind me. The hygienist then began to read off a series of integers, two, two, three, four, two, two, two, three, three,….  It rather reminded me of the number stations that existed (probably still do) on short wave radios. One can tune into them and  listen to what is thought to be some code or cipher meant for some manner of operative.

I thought about it for a moment, and then asked “what are those numbers?”

“They’re pocket measurements of your teeth.”

Predictably I asked “are those values in millimeters?”

“Yes, millimeters.”

She was reading off the values at an astounding pace and the woman with the clipboard behind me was writing down the values. I then had another mystery on my hands.

“How on Earth are you measuring the values so quickly?”

The hygienist replied “oh, the periodontal probe is striped with one millimeter graduations.” She then showed me the probe and I could clearly see the one millimeter dark and light alternating stripes.

My dentist appeared and asked for the results compared with last time. I was rather pleased when she looked at the data and said with surprise “the numbers are all better?”

“Yes, better” the hygienist confirmed.

Unable to contain myself I blurted out “how is this determined from the data?”

To my chagrin, the trio all pointed to the rather large poster in front of me at the end of the dental chair just beyond my feet:

Pocket_Depth_Numbers_PosterThe chart has an image of the periodontal probe I was shown with its graduated dark and light bands. It has a chart, in millimeters, of the depths that are considered healthy in green (1-3 mm), yellow for a depth that will illicit concern (4 mm), and red for a value of 5 mm and beyond.

The simplicity and ease of this measurement had an elegant satisfying feeling. I wish I encountered more situations like this in the US.



Curiosity Makes the Kat

Cheshire_Cat_TennielBy The Metric Maven

Bullcat Edition

My friend Kat generously provides interesting examples that illustrate innumeracy and the foibles of our Ye Olde English irrational grouping of measurements. Long time readers may recall the response offered by the former head of NIST to a We The People Petition requesting we convert to the metric system in the U.S.. In it he said: “if the metric system and U.S. customary system are languages of measurement, then the United States is truly a bilingual nation.” I found this statement abhorrent, misleading and its metaphor designed to substitute politics for measurement. Kat provided a cute quotation I found humorous:

If math is the universal language, then the imperial system must be a speech impediment.

She also told me a tale about her husband and a potato dish he was making. As he was following the recipe, Kat’s husband checked the taste of the potatoes and suddenly realized they were very, very salty. Kat and her spouse investigated the situation and realized that he had confused Tbl with Tsp, and  accidentally introduced three times the amount of salt into the potatoes as was called for by the recipe. I myself, long before I took to a keyboard to write about the metric system, made the teaspoon/tablespoon mistake when cooking—more than once. Rather than questioning our non-system, I blamed myself for not being sharp enough to catch it. My background in magic, informs me that this situation is much like magical illusion, it has nothing to do with your intelligence, it has everything to do with your perception. Tsp versus tbl is a perceptual trap that almost everyone experiences at one time or another.

Kat brought up something that I had personally witnessed, but did not realize had also been documented. The New York Times wrote an article about American innumeracy which contains this nugget:



Upon reading this, I can imagine some denizens of the US might begin sporting a furtive grin and retain an unshakable confidence that “they would never be that dumb.” This American hubris is why we can never reform anything in the US. I had to stop and think about the difference in fractions when I was in a hamburger chain years ago. My significant other was astonished that I had to stop and think about the magnitudes. The truth, which may not be acknowledged in the US, is that “fractions are a notation that does not allow for immediate magnitude comparison.” If you say this in the US, great joy is taken in pronouncing the person stating it to simply be a dumb-ass. When I hear this arrogant attitude that everyone else is an idiot in the US but me, I often think of the movie Idiocracy, where the people in the movie are convinced that a product called Brawndo should be used to irrigate plants, and the reason why is a tagline: “Because Brawndo’s got electrolytes.” and “it’s what plants crave.” When water is suggested as the proper substance for hydrating plants, the idea is met with derision. No controlled experiments or trials. Clearly water is a fluid only suitable for use in a toilet. Never mind the plants are dying, the idea is considered sound without investigation, because “it’s obviously true.”

I stood in line at a burger chain years ago, and heard person after person in line asking one another about the relative sizes of the fractional burgers on the menu board. Is 1/3 bigger than 1/4? I even saw a few people make it to the ordering station and directly ask the cashier which burger is larger. Can you quickly arrange these fractions in ascending order?: 5/8, 1/2, 15/16, 3/4. How about 63, 50, 94, 75? The continued use of fractions in everyday work only demonstrates how tenaciously people will cling to received ideas without ever thinking about them or challenging them. Familiarity bests simplicity. Below is a readout for an automatic feed on a vertical milling machine:

Machine_Shop_DialDoes the use of fractions provide an intuitive feeling for the relative magnitudes of each of the fractions?–no–I would argue they don’t. Hindu-Arabic numerals do. Let’s list 1/4, 1/3, and 1/2 pound hamburgers in grams: 114 grams, 151 grams, 227 grams. Seems straightforward to me. How about 100 grams, 150 grams and 225 grams? Integers are nice.

This graphic from a recipe appeared on metric sites sometime back and illustrates the point yet again:

sQr0hxfYears ago, my father received a really neat device to measure paper and cardboard thicknesses. Here is what it looks like:


The outer scale is in fractions, and the inner is in millimeters. It is not immediately clear to me that 31/64 is between 1/2 and 15/32 of an inch. The preference and inculcated comfort for fractions is illustrated by how they are converted to millimeters. The numbers in millimeters are all out to three places, or 1 micrometer. The fractions are in increments of 1/64 of an inch as one can see from the very first metric increment 0.397 mm. Essentially the digitized graininess of the measurement is about 0.4 mm at best. One could easily round the millimeters to a single place after the decimal point. Here is an abbreviated list of how the paper measuring device could have been labeled:

1/64    0.4 mm
1/32    0.8 mm
3/64    1.2 mm
1/16    1.6 mm
5/64    2.0 mm
3/32    2.4 mm
7/64    2.8 mm
1/8      3.2 mm
9/64    3.6 mm
5/32    4.0 mm
…and so on….

Which set of numbers looks straightforward now? The millimeters are in increments of 0.4 mm or (400 um).

When the metric system was first formalized, Mathematician and early metric system founder Pierre-Simon Laplace (1749-1827) realized how much imposed perceptual prejudice would impede it. Ruth Inez Champagne has this to say in her PhD thesis:

Laplace foresees many difficulties involved in changing the old habits of adults. He tells his students that they will encounter great resistance among those who are familiar with the customary system of measurement. He indicates that the metric system “appears very complicated to them,” because man is naturally inclined to view new things as difficult and complicated because of his habits and prejudices.

Laplace goes on to quote Jean-Jacques Rousseau (1712-1778), who stated: “something known and bad is preferable to a better way that has to be learned.” Perhaps that should be the official motto of the United States when it comes to the metric system.


You can help support this website by purchasing a copy of my new book The Dimensions of The Cosmos Tales from Sixteen Metric Worlds. The book may be purchased here. The book divides the cosmos using 16 metric prefixes into metric “worlds” such as Megaworld, Gigaworld, Picoworld, Nanoworld and so on. Here is the cover and product description:

perf6.000x9.000.inddOriginally, our world was described using a plethora of provincial ad hoc measurement units only of everyday dimensions. The US inch was initially defined as the length of three barleycorn placed end-to-end, and is the current basis of US shoe sizes. The invention of the microscope and telescope in the 17th century revealed unimagined new macroscopic and microscopic worlds. The Dimensions of the Cosmos takes the reader on a tour of these hidden worlds with the only measurement system designed to intuitively describe them, the modern metric system. From metric worlds that describe atoms, viruses, bacteria, quantum dots, and pollen to those which describe planets, solar systems, stars, galaxies and the universe itself, the reader moves from Yoctoworld through Yottaworld. The sizes and stories of these objects are related so the reader experiences the immense diversity and wonder found in our current understanding of the natural world.