I've been looking around quite a bit, and can't find what I want: 1. Show two pulses colliding and superposing 2. In-phase or out-of-phase would be nice 3. Most importantly, to be able to run SLOWLY, so students can easily see how the two pulses build each other (or cancel) 3b. Ideally, to be able to pause the whole thing 4. Be nice if the pulses could be different sizes 5. Must have enough detail that students can clearly see how they add Point #3 is where the couple dozen simulations I looked at fail. If I jiggle the parameters in the pHet string simulator, I can get slow, but it fails #5 because the detail is crude. BONUS ROUND: I've also been looking for a freezable Windows XP oscilloscope program. I want to be able to capture/freeze a waveform-like from a plucked string or struck drum-so that students can calculate the period from the scope scale and thus get the frequency. Thanks!