Ezra Steinberg asked in USMA 19518: >I was surprised (pleasantly) to see in the NIST guidelines linked to in an >earlier >e-mail on the list this morning that they specify the 1 to 1000 rule (e.g. >use 750 >mL instead of 0.75 L). > >Can anyone tell me if this is just a guideline or does it have (even a >little) more >weight than that (maybe even such instances as 0.75 L are illegal?). I ask >because >I've seen such labelling and I'd like to inform the companies that they should >change -- the more weight the NIST document has, the more "ooomph" I can >put in my >correspondence to the companies in question.
NIST Special Publication 811, 1995, says in section 7.9: "It is often recommended that, for ease of understanding, prefix symbols should be chosen in such a way that numerical values are between 0.1 and 1000, and that only prefix symbols that represent the number 10 raised to a power that is a multiple of 3 should be used. ............................................................................... "However, the values of quantities do not always allow this recommendationm to be followed, nor is it mandatory to try to do so. "In a table of values of the same kind of quantities or in a discussion of such values, it is usually recommended that only one prefix symbol should be used even if some of the numerical values are not between 0.1 and 1000. For example, it is often cpnsidered preferable to write "the size of the sample is 10 mm X 3 mm by 0.02 mm" rather than "the size of the sample is 1 cm X 3 mm by 20 um". "In certain kinds of engineering drawings it is customary to express all dimensions in millimeters. This is an example of selecting a prefix based on the practice of a particular field of science or technology." ISO 100-1987 sais: "4.1 The choice of the appropriate multiple (decimal multiple or sub-multiple) of an SI unit is governed by convenience, the multiple chosen for a particular application being the one which will lead to numerical values within a practical range. "4.2 The multiple can usually be chosen so that the numerical values will be between 0.1 and 1000." Joseph B.Reid 17 Glebe Road West Toronto M5P 1C8 Tel. 416 486-6071
