Comments on: Quiz Bowl: SI vs Conventional Units http://blog.amamanualofstyle.com/2012/02/28/quiz-bowl-si-vs-conventional-units/ Official blog of the AMA Manual of Style Tue, 09 Apr 2013 06:05:23 +0000 hourly 1 http://wordpress.com/ By: M R Page http://blog.amamanualofstyle.com/2012/02/28/quiz-bowl-si-vs-conventional-units/#comment-460 Fri, 02 Mar 2012 21:06:14 +0000 http://blog.amamanualofstyle.com/?p=384#comment-460 A big problem with the AMA manual is a lack of consideration significant figures. The conversion factor listed in the online “SI Conversion Tables” section from feet to centimeters is 30. That’s wrong. Let’s say I try to convert my height (6.0000 feet) into centimeters. The “.0000″ means that my measurement has 5 significant figures. Significant figures are important in science and health care.

I start with the only unit conversion between customary and metric that matters: 2.54 centimeters equals exactly 1 inch. This is the only conversion that matters because it is a definition. There are infinite significant figures.

Here is what happens if I use the “SI Conversion Tables” section of the AMA manual of style:

6.0000 feet * 30 = 180 centimeters

Here is what happens if I use math and pay attention to significant figures:

6.0000 feet * (12 inches/1 foot) * (2.54 cm)/(1 inch) = 182.88

Where did those extra 2.88 centimeters come from? They came from a a conversion factor that was wrong.

For the same reason as above, your answer to the first problem is wrong.

7.2 inches^2 * (((2.54 cm)^2)/((1 in)^2)) = 46.45 (assuming 4 significant figures, to demonstrate the inaccuracy of your conversion factor)

This isn’t just an academic exercise. A text for editors shouldn’t have errors like this.

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