Let me just state as a disclaimer first of all that the purpose of this post is not to somehow prove that the US Customary system of measurement is superior to the Système International d'Unites. Au contraire, my goal is to express my opinions as to why the metric system is not necessarily superior to US Customary units.
I should start off by saying that I truly despise those "metric purists" who were born as Americans, but somehow, due to their exposure to academic idealists, have turned into metrosexual Frenchmen prancing around speaking of how nice the weather is when it's 15 degrees out. I can understand if you're from a country that uses metric as its primary system of measure and actually have an anecdotal mindset about what metric values mean, that's all good. But if you're just an invertibrate who follows whatever your professors tell you, you should act like the lemming that you are and jump off a cliff.
The most compelling evidence that I've found in my own experience as an engineering major that the metric system is not particularly superior to US customary units is that the frequency of error is reduced only marginally and the magnitude of error is increased drastically. Due to the ease of using a decimal system in metric, there are some errors which are prevented by use of the metric system. These errors, I've found, are generally made by those who are not paying an incredibly great amount of attention to what they are doing and could often be prevented by more careful analysis. The tradeoff here is that when errors are made in the metric system (and trust me, they are) they are often of much greater magnitude than they would be under the US customary system. I've frequently said that with US customary units errors are generally on the order of a factor of 2-4, while errors made while using the metric system are by factors of 2-4 orders of magnitude, or 100-10000.
To put this in a little bit of perspective, I'll use the anology of structural engineering. Let's say that there's an office building which is supposed to sustain a load of 500 kips or 2.22 MN of force is to be designed. Naturally this building would hold plenty of people and property which is of great worth. Let us now suppose that an error in calulation has been made while using US customary units such that the engineers suppose that the building will only need to sustain 167 kips of force, an error of about 3x. Structural engineers often used what is known as a "safety factor" which essentially multplies the calculated values for load, stress, etc by a set value in order to prevent failure in the case of error. These safety factors are generally between 1.5 and 5 depending on the project. For something like an office building, a factor of about 2.5 would probably be used. As you can probably see, this safety factor will not entirely accomodate for the error in calculation, however, depending on the material, this structure would remain safe for long enough to remove all persons and all essential property, and would probably stand long enough to be demolished and rebuilt.
Now let's assume that the same structure was designed using metric units and a very simple error which is common amonst undergrads is made of saying the building will support 2.22 kN instead of 2.22 MN. In this case, a safety factor has no chance of redeeming the error made by this engineer. The most likely situation is that this structure would collapse while still under construction and kill a relatively few construction workers who were on-site at the time. The worst-case scenario would be that it is able to sustain the dead loading of its own weight, but not able to sustain the live loading of people and furniture, which would indeed be tragic.
At this point you're probably thinking of submitting a comment that reads, "Well William, if the metric system is so inferior in this particular aspect, why aren't buildings collapsing all over Europe and Canada?" And you would be justified, because the failure rates of buildings are very low both in and outside the US. As I already mentioned, the simplicity of the decimal system used in metric helps to moderate both the number and severity of errors which are made. In addition, those who have lived all their lives under the metric system tend to be more proficient than American undergrads who just like the metric system because it requires less mental effort. Finally, I would submit that structural engineers are very good at what they do. These problems are checked and rechecked for accuracy and precision before they are ever submitted to be built.
I submit to you that there is at least one gaping hole in the supposed perfection of the metric system. The magnitude of error which can occur when using metric units is just one piece of evidence that the metric system is not universally superior to US customary units, or any other system of measure.
No comments:
Post a Comment