The user interface on my microwave.
You enter the cooking time is by pressing buttons which correspond to a particular amount of time, which adds that amount of time onto the clock. The available lengths of time are 10 seconds, 30 seconds, 1 minute and 5 minutes
This would be fine if it wasn't for the irritating fact that the 30 button can only be used separately from all the others. So if you want 40 seconds it must be entered as "10,10,10,10"; you can't do "30,10" or "10,30" as the 30 button becomes disabled when any other button is used and vice-versa.
Similarly, 1½ minutes may be entered as "30,30,30" or "1,10,10,10" but not as "1,30"
Who on earth thought this was a good idea?