David, (01)
All units of measure are ultimately defined by some process
of measurement. The meter was formerly defined by a comparison
with a standard held in a vault in Paris. Now it's defined as
a wavelength of light emitted by a certain type of atom under
certain conditions. (02)
There is no difference, in principle, between the definition of
'meter' or the definition of 'standard candle': (03)
The Standard, or International, Candle is a measurement
of light source intensity. It was originally defined as
a one-sixth-pound candle of sperm wax, burning at the rate
of 120 grains per hour. This intensity of light was standardized
in 1921 in terms of incandescent lamps, and candles are no
longer used for reference. (From Britannica online) (04)
The definition of 'hardness' by various methods is no different in
principle from the definition of any other kind of physical unit. (05)
John Sowa (06)
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