Carver County, Minnesota, is in big trouble. (via buzz.mn)

Eric Mattson was not surprised that the small vacant lot he bought last year near the shores of Lake Waconia was increasing in value.

What shocked him was the $189 million market value the Carver County assessor’s office came up with for the 55- by 80-foot lot, making it the most valuable property in Waconia and possibly the county.

Of the resulting $2.5 million tax windfall, about $900,000 had already been spent by the time Mattson got the bill and came in to complain. They’re now looking at spending cuts and new taxes to pay for the shortfall.

“This is not an ‘oops.’ This is a major error that affects an awful lot of people,” said Mark Lundgren, director of the Carver County division that oversees the assessor’s office.

So how could someone make such an egregious error?

Lundgren said the trouble began in August when a clerk went into Mattson’s file to change the designation of the property, at 233 Lake St. E., from homestead to non-homestead to reflect its change in status after its sale.

The clerk filled in the $18,900 proposed valuation, but then mistakenly hit the key to exit the program. The computer added four zeros to fill out the nine numerical spaces required by the software, thus indicating the value was $189,000,000.

So many thing come to mind, most of which are probably too snarky. But a few observations come to mind:

• Don’t just pin this on the clerk. The major mistake was with the programmers, whose software did such an unexpected thing, and on the auditors, who missed a $2.5 million mistake. (Oddly, given that audit failure was an issue, the only solution worth mentioning in the article was “more auditing”.)
• Programmers, cherish your input. Do not auto-munge it without at least user review! And, I’d argue, don’t auto-munge it at all if the result is at all valuable. Validate it, sure, but don’t change it; force the user to fix his or her own mistakes. After all, if your program was so smart as to know what the user “meant”, why does it need manual data entry at all?
• Use modern tools! What kind of data store today requires zero-padding? MySQL is a free download, and very popular; for all its perceived faults, it can at least store numbers of variable sizes correctly.