Phase delay is exactly the opposite of phase advance, i.e., a shift later in time. (Confusion is sometimes introduced into these concepts because clock language is reversed; to effect a phase delay, the clock is moved ahead or advanced. Contrariwise, as in the example in phase advance, the change from the 11 p.m. - 7 a.m. to the 8 p.m. - 4 a.m. position requires a movement of the clock backward.) See Phase advance.