Of course you really don't need this table, for as long as you know what each of the prefixes means you should be able to convert any metric unit of length into another quickly."" This seemingly incidental remark really summarizes what Rahn is about: not setting down terms and figures for memorization, and certainly not recapitulating yet again the system's political history, but explaining what the common units mean, how they were established, and how they work. She begins then at a properly elementary level, enumerating the conveniences of standard units, and ends just as patiently differentiating between weight and mass. Some of the appended definitions, though, are bound to throw readers who need such matters carefully spelled out, and those who don't might become impatient with all the soft information at the center. Supplementary, but a valid alternative approach.