Round-off errors – not the kind of thing the average consumer spends much time worrying about. As an engineer, I was always taught to avoid round-off errors. While developing numerical modeling algorithms (hey, it pays well!), I had to be very careful to make sure round-off errors didn’t unexpectedly bite me in the butt when I wasn’t looking (though sometimes they did anyway). So I was a bit surprised (and a bit disappointed) to see a creative use of round-off error in my own kitchen – a use designed to misinform the average Joe.

Or Jane. The kind of person who thinks statistics are just for sports fanatics and fantasy football freaks. I was using a can of Pam – you know, that spray-on oil for the few people left who don’t own Teflon pans. Now Pam (or any of the many similar products) has exactly two ingredient: vegetable oil and propellant. The propellant is of negligible quantity, so basically it is a can of 100% oil. So I was surprised to see on the nutritional label that a serving of Pam contains 0 calories, 0 grams of fat, and 0% of its calories from fat. So how can a product that is effectively 100% fat be, in fact, fat free?

Round-off error. It seems that the people who regulate these labels decided that it is OK to round to the nearest 1 gram. Thus, if a serving has 2.3 grams of fat, they can just say 2 grams on the label. 12.6 becomes 13. And if the amount of fat, measured in grams, is less than 0.5? Well, you round it down to zero. So if the product is 100% fat, how can the amount of fat be less than 0.5 grams? Why, just make the serving size less than 0.5 grams! By rounding, it has exactly zero of everything! One serving of Pam is a 1/3 second spray, which makes the serving size conveniently less than 0.5 grams.

One-third of a second. I tried this, but I think fast Pam sprays are a young man’s sport. I couldn’t move my finger up and down fast enough to get less than a 3/4 second of spray. Maybe there’s a technique. But anyway, you can see how, through creative rounding, the label was allowed to say 0 grams of fat. That’s bad enough, but what REALLY gets me is the claim that Pam has 0% of its calories from fat! What is zero divided by zero, anyway? According to many high school math students, and ConAgra Foods, the makers of Pam, the answer is zero. Of course, some of us were taught that math works a little differently than that (I won’t go into L’Hopital’s rule, or that you should round your answer only after you have completed all of your calculations). You don’t need a math degree to see that the correct answer, in this case, is 100%, not 0%.

So there you have it. Round-off error biting the average consumer in the butt (which, by the way, may get a little bigger if you take the nutritional label of Pam at face value). I’m glad I paid attention in math class.