Tic

A tic in Doom is a 35th division of a second. Sometimes round-off errors may make this division inexact, but otherwise, consider 35 tics to make a second.

There are also octics, introduced by GZDoom for some of its linedef specials which were imported to Eternity, which are made of eighths of seconds. Given that the game runs on tics, and internally octics are converted to tics, their length is even less exact.