I have strong opinions about the proper UI design for a microwave oven:
The number buttons should just be numbers. Pressing the 2 button should not immediately start cooking for 2 minutes. If I want 2 minutes, I’ll hit 2-0-0-Start. I should not have to find a Time Cook button, or anything like that, before I can heat my food.
There should be a +30sec or +1min button. I don’t really care which, but if I had to choose, I’d probably go with +30sec.
The proper arrangement of the start, stop, and clear functions is Start on one button and Stop/Clear on another button. Pressing the Stop/Clear button once stops the cooking and pauses the timer; pressing it a second time clears the timer.
The beep that signals the end of the cooking time should be loud enough and long enough to get my attention, but it should stop beeping immediately if I open the door or press any buttons—obviously you have my attention, and the alarm has served its purpose.
There should be a kitchen timer mode, and it should be possible and intuitive to cook food and use the kitchen timer at the same time.
When I set it for less than full power, it should be a true partial power mode (PWM?), not 100%-0%-100%-0%-100%-etc. for the specified duty cycle. That’s cheating, and I hate burned popcorn.