Asimov-watchers know his fascination with measurements. They know, too, that he'll always provide some down-home comparison to make a millimetre meaningful. This volume can be said to represent the apotheosis of Asimov as Ruler of Weights and Measures. He has chosen to celebrate the Systeme International d'Unites, known to all metric users as the "SI version." In his compulsive way, Asimov takes the reader up and down assorted ladders of length, area, volume, of mass and density, temperature, time, pressure, and more. He meticulously explains exponential notation at the outset, and goes on to explain the origins of rods, furlongs, acres, and suchlike used in the English system (obsolete, of course, outside England and America). Will this exercise win new friends for litres and metres? (The SI spelling.) Will it persuade Congress or the constituency outside science? Probably not. It will serve as a fine reference for schools, however, and might ease the burden of math and science teachers with its inspired examples: "The population of Rumania would also have a total mass of about 1 megatonne"; "A ray of light would, in a decisecond [0.1 second], travel 30 megametres. This is three-fourths of the distance around the Earth at the equator." There is also a hidden agenda: as Asimov pursues the nuances of space or time he can track the age and extent of the universe, the evolution of species, the dimensions of everything from cells to stars; he can explain mass vs. weight, superpressure, superdensities, superconductivity. . . adding an occasional macabre fillip: "5.27 minutes is about the time it takes for a human being to die of asphyxiation." Readers can best savor the full measure of the book, so to speak, in tasty bits and pieces.