etalon

/ˈiːtəlɑn/
noun
  1. A standard or reference used for comparison or measurement, especially in science or technology.
    • The laboratory uses a precise etalon to calibrate its laser equipment.
    • In optics, an etalon is often made of two parallel mirrors that create interference patterns.
    • The new sensor was tested against a certified etalon to ensure accuracy.
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