How much will some wealthy science buff pay for what Bonhams is calling "one of the greatest scientific instrument discoveries in the world"? On March 21, we'll find out, as the 214-year-old British auction house offers up an almost unimaginably rare 14th-century brass astrolabe quadrant -- a kind of medieval pocket calculator, of which only seven others are known to exist -- discovered by Andrew Linklater of the Canterbury Arachaelogical Trust during a 2005 "archeological watching brief" just beyond the Westgate of Canterbury.

Astrolabe quadrants were used for telling the time, making astrological predictions, and solving mathematical calculations. Being able to properly use one of the instruments, however, was no small feat and in 1391, Geoffrey Chaucer himself wrote a "Treatise on the Astrolabe" (the oldest technical manual in the English language), including sage advice along the lines of:

Rekne and knowe which is the day of thy month, and ley thy rewle up that same day, and than wol the verrey poynt of thy rewle sitten in the bordure upon the degre of thy sonne.

(You know a writer's a genius when even his usage instructions for an astrolabe sound like poetry.)

Even more astonishing than this quadrant's rarity, however, is its size: As the Bonhams Lot Description tells it, "The present example...is quite small, having a radius of only 70mm [roughly three inches]. Of those already known, the average size is 280mm radius [11 inches] and the smallest is 80mm radius." And as we all know, the very, very small often trumps the very, very large at auction.

The quadrant is expected to fetch anywhere from £60,000 to £100,000, or close to $200,000 at the top end of the bidding. (In June 2004 a somewhat similar quadrant, made for pilgrims going to Mecca and Medina, went for $65,000.)

"Nothing like it has been seen at auction before," Bonhams claims of the recently unearthed astrolabe. In a few weeks, we'll see if the little 700-year-old instrument can back up that sort of breathless hype.

-- NIA ELIZABETH SHEPHERD