[Fwd: Risks Digest 20.30]

Joachim Feise (jfeise@ics.uci.edu)
Sat, 17 Apr 1999 21:04:06 -0700

RISKS List Owner wrote:
> RISKS-LIST: Risks-Forum Digest Friday 16 April 1999 Volume 20 : Issue 30
> Date: Thu, 15 Apr 1999 17:50:14 -0400
> From: "Ben Bederson" <bederson@cs.umd.edu>
> Subject: Space character in number causes silent Excel miscalculation
> Error of US$19,130 !
> I have found Microsoft Excel to be very good at mixing different data types
> without having the user to specify those types. However, the fact that the
> types are not specified explicitly pose a risk. I recently had a budget
> submitted and approved that turned out to add up to US$19,130 over what the
> grand total said it did. The problem was that the $19,130 item was actually
> listed as "19, 130" The space character was barely distinguishable on the
> screen (partially because of the use of a proportionally-spaced font and the
> fact that the space was directly after a comma). It was only when I printed
> the spreadsheet later on that I noticed it (after the budget was approved).
> Normally, this error stands out because Excel by default left-justifies text
> and right-justifies numbers. However, I had specifically right-justified
> the column in question earlier. The issue here is that the "19, 130" was
> interpreted by Excel as text rather than as a number. Since Excel doesn't
> generate warnings when adding text, but rather interprets it as 0, I had no
> notification of the problem.
> This is an instance of a general risk in the trade-off that often comes with
> making interactive systems usable in that many mundane tasks are automated
> (such as type specification), and warnings are eliminated resulting in the
> user not knowing how things are interpreted.
> Prof. Ben Bederson, Computer Science Department, HCIL, University of Maryland
> College Park, MD 20742 1-301-405-2764 www.cs.umd.edu/~bederson
"If Gore invented the Internet, I invented spell-check."
- Dan Quayle