Terry Simpson wrote in USMA 22926:
I am under the impression that the CGPM regards 'SI' as equivalent to 'metric'. This is because they use the following phrase: "... the International System of Units (SI), which is the modern form of the metric system;"It does not say: "... the International System of Units (SI), which is the modern *subset* of the metric system;" If a unit is in the 'modern form of the metric system' it is therefore 'SI' and vica versa. A unit that is 'non-SI' must also be not in the 'modern form of the metric system'. A minute is non-SI and is therefore not metric. My problem is that I was surprised when I read that some non-SI units are described as metric. I can't see anywhere in the text of the SI brochure that supports this. http://www.bipm.fr/pdf/si-brochure.pdf Terry Simpson
Look at the BIPM brochure. Table 6 lists litre, tonne, neper and bel, all of them metric units and accepted for use with the SI. Table 8 lists non-SI units currently accepted for use with the SI: hectare, bar, angstrom and barn. Table 9 lists derived CGS units: erg, dyne, poise, stokes, gauss, oersted, maxwell, stilb, phot, and gal. Table 10 list other non-SI units, but which are indisputably metric: rad, rem, gamma, jansky, fermi, and micron.
"The International System of Units (SI), which is the modern form of the metric system" because all physical quantities can be expressed with the 7 SI base units plus the units of plane and solid angle. However, litre is more convenient for volume measurement, the hectare for some area measurements , etc. Table 9 units that I have listed are obsolete, but are definitely metric.
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