awaves expression builder
hi DZC,
this operation is very simple. fist select v(a), then press middle key of your mouse(or press left and right key simultaneous) and drag it to expression window. sencond, click "-" in the oprators. third, use the same opration like the first drag v(b) to the expression window and place it on the right of "-".
fourth, in the result window give a name of v(a)-v(b),such as diffab. then click apply in the expression builder window. the diffab will appear in expressions window.
double click diffab(in expressions window) then the curves of v(a)-v(b) will show in awanwaves.
here is a pdf from hspice avanwaves.