If the calculator is in Reverse Polish mode (which is the default), you should do:

wave - click on one waveform, then the next
Then hit the "-" key
Then hit plot.

Alternatively you can use the algebraic mode (the choice is in a menu - I can't remember what it's called though, and I'm off line), and use a sequence similar to that you gave. One thing to be aware of is that it is a true algebraic calculator, not a hybrid like many calculators are.

Andrew.