* diff compares two plots vector-by-vector, listing only what changed
V1 in 0 DC 1
R1 in out 1k
R2 out 0 1k
.op
.control
  run                    $ -> plot op1 : v(out) = 0.5
  alter r2 2k
  run                    $ -> plot op2 : v(out) = 0.667
  diff op1 op2
.endc
.end