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CALIBRATION STANDARD
An array of tungsten strip lamps in
a spectral radiance measuring
set-up at a PTB lab in Berlin helps
metrologists establish a range of
high temperature reference points
needed for calibrating thermo-
meters and the dissemination of
the kelvin. With increasing tempe-
rature, color and intensity of the
radiation emitted by the glowing
filaments change: the hotter, the
whiter.

[K] ‘The KELVIN, unit of thermo-
dynamic temperature, is the fraction
1/273.16 of the thermodynamic
temperature of the triple point of
water.’