I hate the Toto dual flush toilets that seem to be everywhere now. Literally yesterday Patrick clued me in to how they work. They have 2 flush "settings." I thought maybe they had some sensor that told them what level flush to use, since there aren't 2 buttons for high and low flush, (those ones, like this picture, are much more intuitive). No, you have to push the flush twice rapidly to get the higher power flush. I suspect Donald Norman is not pleased by them any more than I am. One of his principles is that products like doors should not need even one word instruction manuals. So if your door must say "Push" or "Pull" in order for an average person to know how to use it, it's over-designed and impractical.