When Kronos was located on the top of Prospect Hill in Waltham, I would sometimes eat my lunch at the Burger King® fast-food restaurant on nearby Lexington Street, just a bit north of Piety Corner. I often enjoyed a "BK Broiler®" combo, which I think came to only $2.69 at the time. I may not be correctly remembering the price, but what's important for the story, as you will see, is that the price ended in a "9", and the digit before the "9" was even.

So let's say it was $2.69. The cash register added 14 cents for the five percent Massachusetts meals tax, presenting me with a bill for $2.83. I pointed out to the person behind the counter that the meals tax on $2.69 was only 13 cents, so they had charged me a penny too much. Hey, you don't mess with an MIT-trained engineer who can calculate the meals tax in his head. Needless to say, the cashier couldn't deal with this claim, so he called over the manager. The manager didn't seem capable of calculating the sales tax either - he said he could only take the "word" of the register. I paid the $2.83, as it was hardly worth making a fuss over a penny.

Nevertheless, it offended me that the cash register was giving the wrong answer. When the Massachusetts meals tax was exactly five percent (rounded to the nearest penny), it was extremely easy to calculate in your head:

      1. Drop the decimal point and the last digit, e.g. $2.69 → 26 (takes 10%)
      2. If odd, add 1, e.g. 26 → 26 (this is the rounding step)
      3. Take half, e.g. 26 → 13 (halve it to 5%)

I obtained the relevant statute from the Massachusetts Department of Revenue, and verified that my calculation was correct. The law specified a five-cent tax on every full dollar, and contained a chart showing the tax on all amounts less than a dollar, verifying that the tax on 69 cents was three cents, not four (five percent of 69 is 3.45, which rounds to 3). I copied the relevant page of the statute, and the next time I was at the same Burger King, I gave it to the manager. Although he was convinced that I was correct about the amount of the tax, he said that there was nothing he could do about the erroneous charge being printed by the cash register.

That was not a good answer to give a computer programmer. I was certain that the register could be properly programmed to compute the correct tax, even if nobody in the store knew how to do it. And I felt that they should make some effort to fix the problem - not just brush me off. So I called the Massachusetts Department of Revenue to report the problem. I half expected to get a brushoff from them too, because the amounts involved were so small. But they were indeed interested. In fact, I got some idea of how seriously they took it when I was referred to the criminal investigations division, which asked me to send them the register receipts showing the error.

While waiting to see what would happen, I did some lunch-time experiments to scope out the extent of the problem. By buying combinations of various items on the menu, I determined that the extra penny was added only when the total of the bill ended in a "9", and the previous digit was even. This is just one cent below the point at which the tax jumps up by a penny. I also was interested in knowing whether this problem affected many (or even all) of the local Burger King stores, or only the Waltham store on Lexington Street. I checked out the store in the Arsenal Mall, in Watertown, and found that they did not have the problem. I also noted that they had a visibly different type of cash register.

Of course, while doing all this investigating, I was eating a lot of food from Burger King. That was not a problem. I was not angry at Burger King. I was sure that the error was inadvertant, a simple mis-programming of the register, and they could hardly be making a lot of money out of it, a penny at a time, at only one store. And I liked their lunches, even though some of my choices were being driven by a particular check total I was trying to achieve. But still, I had an engineer's desire to see mathematical correctness restored.

After a couple of weeks, the Massachusetts Department of Revenue had evidently struck, and the problem was fixed. But it was not fixed as I expected it would be. My guess is that the Burger King management had not been able to properly re-program the register, because what they did instead was to change all the prices. The $2.69 combo went up to $2.70, and all other odd-numbered prices on the menu went up by a penny. It was no longer possible to generate a total ending in a "9", so the problem was cured. Now, instead of being overcharged by a penny, I found that the price I paid had gone up by two cents (since the tax on $2.70 is legitimately 14 cents, I was now paying $2.84). Bummer!

But I suspected that this fix wouldn't last. Indeed, it wasn't long before the prices started creeping back to what they had been before. Since stores like this change managers all the time, I suspect (although I can't know for sure) that some new manager arrived, looked at the menu, and thought, "Why are these prices different from the corporate standard?". Once the prices were changed back, it was revealed that the register was still mis-calculating the tax. So I once again "dropped a dime", and called the Department of Revenue.

And this time, after a couple of weeks, Burger King finally got it right - their register, the same one as before, was fixed, and started calculating the tax correctly.

Someone I told this story to asked if I was worried that an employee at Burger King might retaliate by spitting in my lunch. After all, the consequences for them might have been no laughing matter. I'm sure that resolving the issue took a certain amount of management time, and for all I know, they were fined for the violation (especially on the second offense). But I really doubt if anyone there had any idea who had turned them in. Weeks had elapsed between the time I had complained to the manager about the error and the time the Commonwealth took action, so I assume that nobody ever connected me to the inspectors showing up. Certainly, nobody ever said a word to me about it, and I doubt if the cashiers and food preparers had any idea at all what was going on.

I always liked Burger King's "BK Broiler", which now seems to be called a "TENDERGRILL® Chicken Sandwich". Try one. But check the tax.

Engineers like me tend to have strong superegos - a well developed sense of right and wrong. We like order in the universe. OK, some of us are marginally obsessive-compulsive. And we like to fix things.

Here's an old engineering joke illustrating these traits. You can find versions of it all over the internet, and I've been unable to figure out who first wrote it, but here's the version I heard:

A soldier, a priest, and an engineer were condemned to die on the guillotine. The soldier went first, and he made an unusual request. He asked to be executed facing up, so he could watch the descending blade, and thus die bravely. The rope was pulled, and the sharp blade screamed downward. But halfway down the track, it screeched to a halt. The crowd roared, and following tradition, the soldier was set free. The priest was next, and following the soldier's lead, he also asked to lie down facing up, so he could die facing heaven. The machine was checked over, and found to be in good working order. Again the rope was pulled, and the blade descended. But again, halfway down the track, it jammed. And so the priest, like the soldier, was set free. The executioners carefully inspected the machine once again, but everything seemed to be in order. They could detect nothing to explain why the blade had stopped. They ran it through its paces several times without a prisoner in place, and it worked flawlessly. Finally, it was the engineer's turn. Like the others, he asked to be executed face-up, so he could see how the mechanism worked. Just as the executioner was about to pull the rope, the engineer called out, "Wait! Wait! I see what the problem is!"