Retrieving "Mercury In Glass Thermometer" from the archives

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1. Instruments

   Linked via "mercury-in-glass thermometer"

   Absolute vs. Secondary Instruments
   Absolute instruments are calibrated directly against fundamental physical constants or units. For example, an absolute gravimeter measures acceleration due to gravity ($g$) based on the measured period of oscillation of a known mass on a calibrated spring, without needing comparison against a [standard artifact](/entri…