alt Hacker NewsThe article suggests a “simple, well-labeled rotary control ... would accomplish the same function” as a power button and “prevent the user from accidentally activating the control in a way that is no longer hidden”. But a rotary control itself has a serious problem, in that it can mislead the user as to the state, on or off. If the power has failed and the machine does not restart when it comes back, the rotary control will remain in the ON state when the machine is off. From memory, Donald Norman called this kind of thing “false affordance” and gave the example of a door that needed to be pulled having a push-plate on it.
So my iMac, among many other devices like the light I wear on my head camping, has a button which you long-press to turn on. It is a very common pattern which most people will have come across, and it’s reasonable to expect people to learn it. The buttons are even labelled with an ISO standard symbol which you are expected to know.
Replies
I have never looked at a fan that isn't running and been confused by the switch being set to “on”. The affordance is that it immediately tells me that the switch is on, so the problem is somewhere else. Compared to the typical phone's “hold for 3 seconds to turn on, hold for 10 seconds to enter some debug mode”, this is a breath of fresh air when anything unusual is going on with the device.
If the power has failed and the machine does not restart when it comes back, the rotary control will remain in the ON state when the machine is off.
A better example may be a solenoid button, used on industrial machinery which should remain off after a power failure, which stays held in when pushed, but pops out when the power is cut. They are not common outside of such machinery, because they're extremely expensive. In the first half of the 20th century, they also saw some use in elevators: https://news.ycombinator.com/item?id=37385826