zero-markhttp://www.oed.com/dictionary/zero-mark_n%3Ftab%3Dmeaning_and_usezero mark, n.
Revised 2018

zero marknoun

  1. 1821–
    a. A mark on a scale or instrument from which a positive or negative quantity is reckoned; b. a mark from which distances along roads or railway lines are measured (cf. zero post n.) (now rare).
    1. 1821
      I have not at present been able to find any correct level of the River Thames, so as to fix the zero marks in London.
      Philosophical Magazine vol. 58 318
    2. 1863
      At the present moment the needle..points to the zero mark on the graduated disc.
      J. Tyndall, Heat i. 3
    3. 1908
      The iron tablet marking the position of Tyburn-gate..is virtually a milestone, marking, as it does, a spot from which the miles on the two great roads that join at Marble Arch are measured. It is perhaps the sole survivor of the zero marks of London.
      Times 2 January 8/6
    4. 1927
      A traveler..will find back of the White House another kind of ‘zero mark’, one which, by Act of Congress, is the starting point of the entire highway system of the United States.
      Popular Science Monthly May 35/1
    5. 2015
      The thermometer was still hovering around the zero mark at kick-off.
      Daily Mirror (Ireland) (Nexis) 14 December (Sports section) 38

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

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