I can't help but notre with amusement the following from the Guardian:

A 118-year-old cylinder that has been the international prototype for the metric mass, and kept under lock and key outside Paris, is mysteriously losing its weight - if ever so slightly.

Physicist Richard Davis of the International Bureau of Weights and Measures in S?©vres, south-west of Paris, says the reference kilo appears to have lost 50 micrograms - roughly equivalent to the weight of a fingerprint - compared with the average of dozens of copies.

"The mystery is that they were all made of the same material, and many were made at the same time and kept under the same conditions, and yet the masses among them are slowly drifting apart," said Mr Davis yesterday in a telephone interview. "We don't really have a good hypothesis for it."

And accountants ask for certainty in tax! No hope, not when even a kilo changes its weight over time.