and 
between: two oscillations with the same angular frequency and
is determined: by their phase difference 
if 
it is said that 
lags 
by 
if 
it is said that is in phase with 
if 
it is said that leads by 
if 
it is said that is in anti-phase with 
For values of 
outside the range 
an appropriate integer multiple of 2 
should be added to or subtracted from to bring it within that range. [P5.4]
may also be applied: to waves at a common point (or possibly at separate points) by comparing the oscillations caused by the waves at the relevant point(s).
Copyright 1997, The Open University