Tag Archives: Metric System

Exactly how big is a kg?

Standards fascinate me. One of the most problematic standard in use almost universally today is the kilogram (kg). The problem is that no one really knows exactly how much mass a kilogram actually has. By extension that means that no one knows how heavy a pound is either since the US government defines it in relationship to the SI kg unit.

Originally the metric system was supposed to be defined in terms of “natural laws” that the common man could measure for himself. The kg was originally defined as a cubic decimeter of water under certain conditions. This is probably what you were taught in school, one of many metric misconceptions (see why everything you know about the metric system is wrong).

But that approach was jettisoned as impractical due to variations in water density, temperature, etc. In 1889 the standard became defined by a set of “physical prototypes” that were manufactured and distributed to major countries. So what was a standard based on “natural laws” became based on an arbitrary hunk of platinum and iridium.

Only that has not worked either (at least not to the number of significant digits desired). The problem is that the different physical prototypes are changing mass by a small but measurable amount. So today there is effectively no precise consistent definition of a kilogram, and thus by extension the pound.

The plan going forwards is to define the kg in terms of basic physical properties, similar to what has been done with the meter and the second. But for now, kg is only an estimate for given levels of precision.


When what you are taught isn’t true

I get a steady stream of indignant sputtering about this post on the metric system and what it means for authentication. One common point that readers make is that Celsius is better than Fahrenheit because it is based on natural law, defined as 100 degrees between the freezing and boiling point of water.

Only it isn’t, and hasn’t been for some time (at least not since 1954). While the freezing point and boiling point of water was precise enough in the 1700’s, it is no where near precise enough to act as a standard. The reason is that no two samples of water will melt and freeze at the same temperature due to variations in water purity, air pressure, and humidity.

By international convention, the Celsius scale is defined by a range between absolute zero and the thermodynamic triple point of Vienna Standard Mean Ocean Water (VSMOW). This point, by the way, is 0.01 C. And VSMOW is not ocean water  (despite it’s name), but rather is a carefully crafted lab concoction comprised of specially defined proportions of oxygen and hydrogen isotopes.

So while we are taught Celsius is defined by the freezing and boiling points of water, it is actually defined by absolute zero (which doesn’t exist in the natural world), and the triple point of a form of water that only exists in the lab.

Explain to me again, why this is less arbitrary that Fahrenheit?

And why is it still taught incorrectly in schools (at least in the US)?

Why everything you know about the Metric System is wrong and what it means for Identity Systems

Recently as part of my work with Cub Scouts I had to prepare a lesson on the Metric System. That started me thinking about the myths and misconceptions of the Metric System, why it isn’t used in the United States, and what that all means for Identity Systems.

First let me say I am a big fan of the metric system (I have a MS in Aerospace Engineering). And living in the United States, I almost never use it. And those not contradictory statements. The reason that I never use it is that for my day to day life outside of work it simply offers no advantages to me. When studying engineering in college I used the Metric System almost exclusively. However after going into the software industry I haven’t used it professionally since.

Here are some myths and misconceptions:

Myth #1 – The Metric System is a base10 system which is far superior to base 12 systems. The metric system has been adopted world-wide (except for those crazy stuborn Americans) because of the inherent superiority of base10 mathematics in every day use.

BTW, what time is it where you are? What coordinates does your GPS show? How steep is that incline? Have you ever tried to saw a 1 meter board into 6 even pieces?

The point is while base10 is much better for doing calculations with a calculator, base12 is better for some calculations you need to do in your head. That is because 10 is divisible by only 5 and 2, where as 12 is divisible by 2,3,4, and 6.

Myth #2 – You shouldn’t use the English (Customary) System for technical purposes because the conversion between feet and inches and pound and ounces is much harder than converting between meters and kilometers and liters and milliliters.

When doing technical work you don’t ever need to convert between feet and inches. You really every need to convert between meters and kilometers either. Once you are using scientific notation it doesn’t matter. 10,000 feet is 1x10E6 feet and 10,000 meters is 1x10E6 meters. Neither unit system is easier than the other in scientific notation.

Myth #3 – The Metric System is superior because all units are derived and reproducible from the properties of natures. For instance the Celsius 0 and 100 are freezing and boiling point of water. The meter is derived from a Meridian of the Earth.

While the Metric System was once naturally derivable, it was long ago discovered that physical properties that they originally used vary too much to give an accurate definition.  For a while they where defined against physical models (for instance a certain platinum bar was used to define the meter). That was eventually viewed as too risky. Now all units are defined in purely arbitrary, but reproducible terms.

Myth #4 – The stubborn Americans will eventually convert when enough are “educated sufficiently”. It’s only ignorance that keeps the Americans from converting willingly like the rest of the world.

The Metric System originally became accepted only at gun point. The point of Napoleon’s guns to be exact. The real telling point comes from the Wiki entry:

As of 2007 only three countries, the United States, Liberia, and Myanmar (Burma) had not mandated the metric system upon their populace.

Ah, breathe in the Orwellian goodness of that statement. The Metric System is so superior to other forms of measurement it has been mandated on the people by the force of law. All for their own good of course.

The point is while there is a huge advantage to everyone being on the same system of measurement, the choice of Metric versus Customary is purely an arbitrary choice. Since people make these choices based on personally perceived value combined with a natural resistance to change, most will not willingly convert to a new system without being forced to under threat of punishment. Or put simply:

Change is hard. Inches are easy.

What does all of this have to do with Identity Systems? Change is painful. Like measurement systems, people will make do with their current Identity System (mostly user IDs and passwords), because they understand it and it works sufficient for their day-to-day lives.

Yes, it’s a mess. Yes, it’s not very secure. But it works for most people. They understand it. They are comfortable with it. Most will not switch to an alternative like OpenID or CardSpace unless they see real value. Or put simply:

Change is hard. Passwords are easy.