The Universe of Discourse

Thu, 26 Apr 2007

Excessive precision
You sometimes read news articles that say that some object is 98.42 feet tall, and it is clear what happened was that the object was originally reported to be 30 meters tall, and some knucklehead translated 30 meters to 98.42 feet, instead of to 100 feet as they should have.

Finding a real example for you was easy: I just did Google search for "62.14 miles", and got this little jewel:

Tsunami waves can be up to 62.14 miles long! They can also be about three feet high in the middle of the ocean. Because of its strong underwater energetic force, the tsunami can rise up to 90 feet, in extreme cases, when they hit the shore! Tsunami waves act like shallow water waves because they are so long. Because it is so long, it can last an hour. In the Pacific Ocean, a tsunami moves 60.96 feet a second, passing through water that is around 1219.2 feet deep.


The 60.96 feet per second is actually 100 km/hr, but I'm not sure what's going on with the 1219.2 feet deep. Is it 1/5 nautical mile? But that would be strange. [ Addendum 20070428: the explanation.]

Here's another delightful example:

The MiniC.A.T. is very cost-efficient to operate. According to MDI, it costs less than one dollar per 62.14 miles... Given the absence of combustion and the fact that the MiniC.A.T. runs on vegetable oil, oil changes are only necessary every 31,068 miles.


(I should add that many of the hits for "62.14 miles" were perfectly legitimate. Many concerned 100-km bicycle races, or the conditions for winning the X-prize. In both cases the distance is in fact 62.14 miles, not 62.13 or 62.15, and the precision is warranted. But I digress.)

(Long ago there was a parody of the New York Times which included a parody sports section that announced "FOOTBALL TO GO METRIC". The article revealed that after the change, the end zones would be placed 91.44 meters apart...)

Anyway, similar knuckleheadedness occurs in the well-known value of 98.6 degrees Fahrenheit for normal human body temperature. Human body temperature varies from individual to individual, and by a couple of degrees over the course of the day, so citing the "normal" temperature to a tenth of a degree is ridiculous. The same thing happened here as with the 62.14-mile tsunami. Normal human body temperature was determined to be around 37 degrees Celsius, and then some knucklehead translated 37°C to 98.6°F instead of to 98°F.

When our daughter Katara was on the way, Lorrie and I took a bunch of classes on baby care. Several of these emphasized that the maximum safe spacing for the bars of a crib, rails of a banister, etc., was two and three-eighths inches. I was skeptical, and at one of these classes I was foolish enough to ask if that precision were really required: was two and one-half inches significantly less safe? How about two and seven-sixteenths inches? The answer was immediate and unequivocal: two and one-half inches was too far apart for safety; two and three-eighths inches is the maximum safe distance.

All the baby care books say the same thing. (For example...)

But two and three-eighths inches is 6.0325 cm, so draw your own conclusion about what happened here.

[ Addendum 20070430: 60.96 feet per second is nothing like 100 km/hr, and I have no idea why I said it was. The 60.96 feet per second appears to be a backwards conversion of 200 m/s to ft/s, multiplying by 3.048 instead of dividing. As Scott turner noted a few days ago, a similar error occurs in the conversion of meters to feet in the "1219.2 feet deep" clause. ]

[ Addendum 20220124: the proper spacing of crib slats ]

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