zero-planehttp://www.oed.com/dictionary/zero-plane_n%3Ftab%3Dmeaning_and_usezero plane, n.
Revised 2018

zero planenoun

  1. 1842–
    A plane (plane n.3 1a) from or against which measurements or comparisons are made.
    1. 1842
      Where v is the temperature at the time t, of a point at the distance x from a fixed plane, which, for brevity, may be called the zero plane.
      Cambridge Mathematical Journal vol. 3 170
    2. 1880
      The zero plane is the surface of the ellipsoid similar to the sea surface.
      S. Haughton, Six Lectures on Physical Geography ii. 51
    3. 2015
      Two coronal and two horizontal zero planes are used as reference planes in these drawings.
      G. Paxinos & C. Watson, Rat Brain Stereotactic Coordinates (ed. 7) p. xii/1

Originally published as part of the entry for zero, n. & adj.

zero, n. & adj. was revised in June 2018.