Last week’s column about the error rate of the state system that scans license plates and generates bills for people using toll roads and bridges had an error of its own. The state Department of Transportation said the rate was one-thousandth of 1 percent. When multiplying the number of toll transactions, which was 35 million in 2014, I used .001. But that left out two zeros behind the decimal point, to account for the 1 percent, which, as most 5th graders can tell you, is .01.

So I should have multiplied by .00001, which means the number of mistakes would be in the range of 350. So hundreds, not thousands of drivers a year who could, like me, get a bill for someone else’s toll.

One reader who is much better at math wrote to correct mine, and point out that by getting two such bills, I was even more special than I thought.

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