|One of our dual flush controls, earlier
Take, for example, the dual flush control illustrated, on one of our toilets (yes, we have more than one - aren't we des res?). Clearly there is a big friendly button and a smaller rectangular bit. My guess is that pressing the big button without the rectangular bit is a small flush, but pressing it with the rectangular bit is a large flush. But it is a guess, because there is nothing about the controls that indicates what they do. There's no reason why, for instance, pressing both shouldn't mean 'special economy flush'.
It's also a guess because, frankly, there is no obvious distinction to the amount of water that flows whether you press just the big button or both of them. In fact I sometimes suspect toilet manufacturers don't fit dual flush at all - they just fit dual buttons and hope no one notices that they don't do anything different.
Failing to make controls obvious is a common enough design fault. Think, for instance, of the controls of a four burner cooker hob. Usually the hob is arranged with the burners in a rectangular array, but nine out of ten times, the controls are in a nice straight line. Because the designer thought it looked neat. But this means it is impossible to deduce which control is for which burner - and the manufacturer accordingly has to give us an instruction book, in the form of little graphics we have to check to see which control does what. If they had put the controls in a rectangle too, there would be no need for instructions.
In the case of dual flush, the design is doubly disastrous, because not only is not obvious what to do, there usually isn't even a graphic to instruction you what the controls mean. It's guesswork all the way. It's easy enough to design a triple flush with no instructions. You have a big button split in half unevenly. The small part does a small flush, the big part does a big flush and pressing the whole does a royal flush. It's a little harder to design a dual flush control that is obvious from the shape of the control on its own, though I believe it is possible, but simply engraving a + on the square button (if that's what it means) would at least bring the flush control up to the level of a cooker.
Come on, sanitary ware gurus. Get your fingers out.