A clock for math whizzes

Update 7:40 p.m. PST January 6: Thanks to alert reader OneGB for supplying the origin of the clock. The central design may look like a bungled biohazard symbol, but it in fact is another three-nine reference, the "hurricane" symbol of a high-IQ organization called the Triple Nine Society. The group also sells Triple Nine aprons, mugs, bibs, underwear, and other whatnot at CafePress.com.

(Credit: Dean Hunt, StreetLessons)

Math enthusiasts who don't want to move totally into the digital realm might appreciate this analog clock.

Each number is expressed as a calculation involving three instances of the number 9.

For example, 5 o'clock is the square root of nine (3), factorial (3x2x1 = 6), minus 9/9 (6-1 = 5).

The trickiest time is 7 o'clock, whose calculation works out to 6.99999..., with an infinite number of nines. Wikipedia assures us that 0.99999... really does equal 1, so no worries that the clock is cheating there.

While we're on the subject of archaic clock technology, how come clocks and watches with Roman numerals represent 4 o'clock with IIII rather than the traditional IV? A friend told me it was because it was easier for illiterate people to comprehend, but I'd love to see some history about this.

(Via Bad Astronomy Blog.)