I still have a dissolve unit. My current configuration only controls two projectors but this particular unit has (had?) add-ons allowing it to go up to 9 projectors at a time. This one is programmable but the previous versions I had were programmed LIVE. You mess up, you start over! You could get anywhere from a cut to a dissolve of several seconds. Interestingly, you could also have one projector hold while the other projector changed several times allowing a constant background over several slides. Then you hit the reset button and all projectors return to the starting position.