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The Soap Box

September 7, 2000
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A few thoughts on metric.

I guess everyone but me was anxious as hell to "go metric." That is, until one day last winter when I had plenty of spare time, I read "Dilemma of Dimensions" in the October 1996 issue of POB.

In that article, the author said the meter was originally defined as a "unit of length equivalent to one ten-millionth of the length of a quadrant of the meridian through Paris, from the equator to the North Pole."

In 1927, the meter was defined as "equaling 1,553,164.13 wavelengths of the red clay of cadmium vapor in dry air, at a temperature of 15 degrees Celsius, at a pressure of 760 millimeters of mercury under normal conditions of gravity."

By the 1960s, the meter was defined as "1,650,763.73 times the wavelength of orange light emitted when a gas consisting of pure Krypton isotope of the mass number 86 is excited in an electrical discharge."

"Wow," I thought, "the meter must be the only thing we know for sure." Then, to confirm my thoughts, I read a letter by Professor C. Merry (January 1997 POB) and was convinced.

I decided to perform an experiment with my EDM to find out just for sure, if indeed the meter is now officially-as Professor Merry wrote-"the length of the path traveled by light in a vacuum during a time interval of 1/299792458th of a second."

In order to create the necessary vacuum, I set up my fans in the garage, each blowing outward through all the openings. Some of the openings were rather small, needing funnels placed in them to direct the air outward. After a while, all the air was gone and my next task was to locate two points on the garage floor exactly 10 meters apart.

I moved a fan at one opening so a ray of light could strike the floor, and I marked the spot with the point of a pin I had removed from a new shirt I bought at K-Mart. I then quickly covered and uncovered other openings until I found one that shone exactly 10 meters from the first spot. I double-checked by deflecting the light from the first hole onto the second spot. This was not too difficult, and I knew how exact it was because I had multiplied 1/299792458 by 10, which was exactly how much longer it took the ray to strike the second spot than the first. And, since I was in the vacuum I had created, the distance had to be correct.

Next, I set my prism (a Topcon single M/2 zero constant 60 mm with ±2 arc second accuracy, (Topcon America Corp., Paramus, N.J.)) over one of the points, and knowing the importance of accuracy, I fine-tuned my optical plumb tribrach to perfection. I then set my Topcon GTS-301 over the other point, checking to be sure it was set to read in meters and the horizontal read-out switch was set correctly. Holding my breath (which was necessary, as I was in a vacuum), I punched the measure button. EUREKA! It read 10 m!

What peace of mind I now have knowing my EDM is accurate. Who needs a calibrated base line? Besides, even though the calibrated base lines are measured perfectly, the ones established before 1983 are no good because they used something other than a meter to establish them. Just do what I did, and you'll be in good shape. You can't use my garage though, because something happened to it (possibly due to the vacuum I created).

And never fear. We may be unanimous in wanting to "go metric" because the Europeans are doing it (we want to be their friends). Our omnipotent government, in its need to decide for us that metric is best, has also decided that NAFTA is now necessary (we want to be its friend too). But, from time to time, we will still (as much as we hate to do it) have to decipher an occasional description or plat with measurements in those old, inaccurate, difficult-to-use feet, or even (heaven forbid!) follow the footsteps of an uninformed surveyor who used chains and links! Just convert them to wonderful, totally accurate, easy-to-use METERS.

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