Dietary Intake

Greg Ingersoll

Mon 11 March 2013 - 14:10:00 CDT

#requirements #optics #physics

I was reviewing customer requirements on a recent project, and we came across something unintentionally comical. There was a requirement for illumination intensity which is given as power per unit area, in this case microwatts per square centimeter (uW/cm^2). The problem was that the m was missing leaving uW/c^2.

6 ounces of cake over 10 minutes is roughly 0.28g/s.

Now c is not a unit, but in the context of light, it represents the speed of light with units of meters per second. Just for fun, I plugged this into Wolfram Alpha as “500uW/c^2”. This reduced to having units of kilograms per second which the tool interpreted as “recommended dietary intake”!

This instance was an obvious typo, but it does highlight the need to be careful when authoring and reviewing requirements. Missing a digit, for example, could have far-reaching consequences for your project. And completely wrong units can cause your Mars probe to crash. Better to catch these things early.

And while we‘re on the subject, what do you use for requirements management? I’m guessing Word/Excel is a popular answer. Leave a comment below. This is a topic I will be covering in future posts.

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