How should the phase arrows be interpreted?

The phase arrows show the relative phasing of two time series in question. This can also be interpreted as a lead#lag. How it should be interpreted is best illustrated by example:

figure('color',[1 1 1])
t=(1:200)';
X=sin(t);
Y=sin(t-1); %X leads Y.
xwt([t X],[t Y]); % phase arrows points south east

Phase arrows pointing * right: in-phase * left: anti-phase * down: X leading Y by 90 degrees * up: Y leading X by 90 degrees

Note: interpreting the phase as a lead(#lag) should always be done with care. A lead of 90 degrees can also be interpreted as a lag of 270 degrees or a lag of 90 degrees relative to the anti-phase (opposite sign).