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Bug or Feature?

© 2012 By: Dov Trietsch. All rights reserved.

I was born in a time and place where avant-garde accountants used a handle-powered adding machines, old-fashioned ones still used pencil and paper, and all used their heads. As a child I did most of my calculations mentally and reverted to paper and pencil only for the really tough ones. As a young statistician I did most of my calculations on an Electro-mechanical calculator which had the ability to do the sum of x while computing the sum of x2. This feature on my "Facit" really facilitated my work because the two sums are needed to compute the average and standard deviation.. I also learned to program computers, but I still do most calculations in my head.

When my daughter started elementary school, the HP hand-held scientific calculator was two years old and K&E stopped making slide rules. When she reached second grade, TI released its "Professor" – an owl shaped hand-held calculator that could also be used to give a child an arithmetic quiz. Almost every kid in her class owned one of these owls and she wanted one badly. Like a banker who’ll only lend money to those who don’t need it, I refused her. "When you know your arithmetic down pat," I said "and need to do really complex computations, I’ll buy you one." Seven years later, for her honors physics lab, I bought her a programmable scientific calculator. Ours, I am proud to say, was a Spartan home. We still don’t have cable TV, we never had any video games and for her personal computer our daughter had to program her own games. She realized, after successfully programming her first Dungeons and Dragons game that she does not particularly like programming, but she was exposed to the art at a very young age and her computer generated game scenarios always drew a crowd of youngsters to our home.

Yesterday, contrary to my habits, I used the Windows' Calculator and out of curiosity used the various keys and buttons. One such button - Int - calculates the integer part of a number. Its inverse - Frac calculates the fractional part. Again, out of curiosity, I tried them both on the number (-5.7). The results were -5 and -0.7 respectively. For 5.7 the result were 5 and 0.7 respectively. This is wrong! Worse, most of today’s young adults, who never mastered arithmetic (because they owned a "professor" or a similar crutch), use the Windows Calculator as a gospel. To them it must be right.

Why is it wrong? The Int function returns the highest integer that is lower or equal to a number. Int(5.7) is indeed 5. Int(-5.7) is (-6). (-5) is greater than (-5.7). The fractional part is even more complex. Again for 5.7 the result is indeed 0.7. For (-5.7) the result is 0.3. Yes 3/10ths! Why? The sum of integer and fraction make the number. 5 + 0.7 = 5.7. Similarly (-6) + 0.3 = (-5.7).

Even at Microsoft they know better. Here is How Excel applies the INT function: =INT(-5.7) returned the correct answer of -6. Excel does not have the Frac function so it could not be tested.

I first noticed this bug in the good old days of Win 3.1. During the years, I have revisited the calculator now and then. At least 17 years have passed. Operating systems came and went. We are now using Windows 7 (8 is just around the corner), but the Int nad Frac error persists. By now it had become a tradition and we all know that tradition is stronger than science. When will they ever learn?! 

 That's All Folks

Posted on Friday, December 23, 2011 7:56 AM | Back to top

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