DYKT: Did You Know That ...

"You, in this country, are subjected to the British insularity in weights and measures; you use the foot and inch and yard. I am obligated to use that system, but I apologize to you for doing so because it is so inconvenient, and I hope all Americans will do everything in their power to introduce the French metrical system ... I look upon our English system as a wickedly brain destroying piece of bondage under which we suffer. The reason why we continue to use it is the imaginary difficulty of making a change, and nothing else; but I do not think in America that any such difficulty should stand in the way of adopting so splendidly useful a reform."
Excerpt from a lecture delivered by Lord Kelvin (William Thomson) in Philadelphia, 29 September 1884
“It is safe to say that after the metric system has been adopted by the U.S. and our people have become accustomed to its use we would no more dream of going back to the present system of weights and measures than we would think of carrying on the processes of arithmetic through the medium of the old Roman letters in place of the Arabic numerals we now employ.”
Alexander Graham Bell, 1906
Metric foes often argue that we should keep our traditional units because Americans understand them. But a recent survey refutes that notion. While Americans' knowledge of SI leaves much to be desired, they seem to understand metric units a heck of a lot better than gallons, fluid ounces, inch fractions, and other antiquated units. A simple 30question test on everyday measuring unitshalf SI and half inchpoundwas given to all students and faculty at an Arizona high school. The median score on SI units was 55% for students and 64% for adults, while the median on inchpound units was only 16% for students and 34% for adults. Twothirds of the students (and 83% of the adults) could read a metric ruler to the nearest millimeter. But only 20% of the students and (73% of the adults) could read an inch ruler to the nearest 16th. Curiously, most students treated the inch fractions as decimals, mistaking the 1/16 inch marks for 0.1 or 0.05 inch marks. For example, they often misread the measurement 2 11/16 inches as 2.8 or 2.65 inches.
Threequarters of both students and adults knew that a liter measures volume and equals 1000 mL (cm^{3}). However, not one person knew the definition of a U.S. gallon (231 cu in.), acre (43,560 sq ft.), or U.S. bushel (2150 cu in.). Most estimates were wildly off. Only 6% of the students (and half of the adults) knew that a U.S. quart is 32 fluid ounces. Twothirds of both students and adults knew the meaning of the prefixes kilo, milli, and mega, and were able to apply them to specific units (for example, 1000 mg = 1 g, 1000 g = 1 kg, 1 km = 1000 m). Most students (and 77% of the adults) could estimate the distance to a nearby city in kilometers. By contrast, only 30% of the students (but 63% of the adults) knew that a [statute] mile is 5280 feet.
Most respondents recognized that an average man is about 75 kg, although only 20% knew that water is 1 kg/L. On the other hand, most students did not know that a pound is 16 ounces [avoirdupois] or that a [short] ton is 2000 pounds. Not one student or adult knew that a gallon of water is approximately 8.3 pounds. About 70% of the students (and 89% of the adults) knew that water freezes at 0 °C, while only half of the students (but 87% of the adults) knew water's freezing point in Fahrenheit (32 °F).
Back in 1974, when I was a pharmacy student taking a course in pharmaceutical calculations, pharmacists were taught that they were inheriting not one, but three, systems of measurement for their professional use: avoirdupois, apothecary, and metric. I soon came to realize not only which system was the best of the three, but also which two systems (avoirdupois and apothecary) were insults to the dignity of the professional cadre of which I was soon to be a part.
It was at that moment in time that the Metric Conversion Act of 1975 was being debated in Congress. I was so moved by my calculations that I met with some of my student colleagues in an open class session to "lobby" for the bill. We were disappointed, though, that the bill was watered down from its original target of mandatory 10year conversion.
Standards abound in my healthcare profession: Joint Commission standards, some measurement standards, legal standards, procedural standards. We are awash with them. But it never ceases to amaze me that when it comes to a universal standard of measurement, we American healthcare folks are still using the WOMBAT (Way Of Measuring Badly in America Today) measurement system.
When I enter a patient's height and weight into the computer at work, I must obtain and enter it in WOMBAT, and the computer converts it to the centimeters and kilograms it is supposed to be in. I can't ask patients how many centimeters tall they are; they just don't know. An established standard of measurement is essential to any modern nation, and certainly should be required by the one nation which claims to set the standards for so many things in the world: the U.S.
Most people do not realize that the standardization of the inch for worldwide use did not occur until 1959. Prior to that the inch had been defined differently among the major inchusing countries: the U.S., Great Britain, and Canada. Each of those countries had their own definition of the inch, and in each case the inch was defined in terms of metric units, the only set of internationallyaccepted standards of length, mass, etc.
In the U.S. the metric system was made legal for all purposes, by the Metric Act of 1866, long before any law defined our common U.S. measures. Later, the Mendenhall Order of 1893 defined our common nonmetric units in terms of metric units. That law regarded metric units as the fundamental and internationallyaccepted standards for the U.S. It was this law that formally defined the inch based on the conversion factor of 39.37 inches = 1 meter as stated in the Act of 1866. This ratio gives an inch approximately equal to 25.40005 mm.
In Great Britain the National Physical Laboratory made comparisons of the Imperial Standard Yard to the International Meter, which yielded differing values for the inch over the years. The 1922 value of 25.399956 mm per inch by was arbitrarily selected for use in calibrating the most precise measuring devices.
The Canadian Parliament in 1951 established their inch based on a legal definition of the yard as 0.9144 m. This ratio defined the inch as 25.4 mm, a third definition of the inch. The Canadian inch was about 2 parts in 10^{6} smaller than the U.S. standard and about 2 parts in 10^{6} larger than the British standard.
The differences in definitions of the inch were enough to cause confusion, inefficiencies, and difficulties during World War II in attempts to interchange various precision products. It was not until later, in 1959, that the definition of the inch was standardized worldwide as 25.4 millimeters exactly.
But that agreement has not completely solved all the problems caused by differing values for the inch. A problem still exists for the foot, where the international foot (based on the 25.4 mm inch) and the survey foot (based on the 25.40005 mm inch) are both still in use. The Coast and Geodetic Survey continues to use the survey foot, whereas the rest of industry uses the 25.4 mm inch. This leaves us with two definitions of the mile, one based on the international foot and the other based on the survey foot. Although this may not seem like much, it causes the two miles to differ by about 3.2 mm (1/8 inch), or in 100 miles to differ by about 32 cm (over one foot)!
Thanks to the work of the early pioneers of aerology, the units used for meteorological measurements of the upper atmosphere were largely standardized long before those measurements became routine. In particular, there is one system of upperair pressure units, unlike we see for surface weather measurements.
Much of the groundwork for the standardization of these upperair measurements was due to Wilhelm Bjerknes (18621951), a pioneer of modern meteorology best known along with his son, Jakob, for the airmass and polarfront theory of cyclones.
One of Bjerknes' contributions to meteorology was his push for widespread use of the CGS (centimeter, gram, second) system of units in meteorology. This was an early version of the metric system that later took second place to the MKS (meter, kilogram, second) system in the development of the International System of Units (SI).
The pressure unit in the CGS system is the bar, defined as one million (10^{6}) dynes per square centimeter, a value approximately equal to the standard atmospheric pressure at the surface of the earth. The bar is subdivided into 1000 millibars (hectopascals in SI) to measure surface and upperair pressures. The use of the bar might not have been common without Bjerknes' insistence. He succeeded at having these rational units be recommended for all uses in aerology by the International Meteorological Committee at their meeting in Rome in 1913. This resulted in the use of the millibar, rather than the millimeter of mercury (Hg) for upperair pressures. The millimeter of Hg was used for surface pressures throughout most of the world, and in the U.S. the inch of Hg was and still is common.
To promote his idea, Bjerknes showed that the use of the bar/millibar was more logical and was required for a strict application of CGS units. Had the millimeter of mercury been used, it would have been necessary to introduce a conversion factor of 1.333 millibars per millimeter of Hg in order to balance units in the dynamic equations of the atmosphere. The millibar made the equations coherent or without the need for such numerical factors in multiplication and division among units.
Bjerknes was forward thinking in pushing for the full adoption of the CGS system, which at the time was the best system for meteorology. He predicted that the universal application of CGS could not be prevented in the long run. At least he was right about the use of a universal system of metric units, not necessarily about the CGS system. Bjerknes thought it unfortunate that synoptic meteorology had not adopted the unit of pressure of the CGS system from its inception. He would have liked to see a universal change of all surface pressure readings to millibars, rather than the pressure related to a column of mercury. But he realized that the time was not right since the world's measurement systems were far from standardized. His suggestion was to await the time when the transfer to one system of meteorological units could become truly universal, "the time when the British Empire and the U.S. shall have adopted the metric system."
It was not until this century that balloons were regularly used to gather upperair meteorological measurements. And our present network of upperair balloon radio soundings (radiosondes) was established during World War II. Few people realize that because of some of the early weather pioneers, there is standardization in the measurement of upperair pressures, unlike there is for surface weather. Upperair temperatures are also standardized in degrees Celsius worldwide. Variations occur for surface temperatures only, with the U.S. the sole user of the degrees Fahrenheit scale. However, complete universality is not unthinkable should the United States convert since it is the only nation still officially using nonmetric units for measurements of the weather.
Back to USMA home.