# Why do some timers require turn past?

Why do some timers require the user to turn past a number before setting the time? The user can choose a shorter time, after turning past the number. Is it a mechanical spring thing?

yes it has to have the spring wound a minimum amount to work correctly.

I think it’s a hysteresis thing. Like if you want to bend a straight wire to 90 degrees, you have to bend it more than that, and it’ll spring back to 90.

It’s using a spring though. That shouldn’t exhibit much hysteresis. It will just start slowing down as it approaches zero, and won’t have enough tension left to operate the timing mechanism unless it’s tightened more than the distance needed to set it. I assume it also lengthens the life of the spring by having the tension released when it hits zero instead of maintaining extra tension on the spring all the time. I don’t know what the timing mechanism. I guess you could tell if it was a simple pendulum and catch mechanism by turning the timer on it’s side or upside down. If it doesn’t operate, or keep time right, it’s probably a simple pendulum mechanism.

Oh because when turning back after turning past, the first part feels easier to turn, before you feel the spring winding. Then again, we might be talking about the same thing. Maybe hysteresis isn’t the correct word.

I don’t if hysteresis is right because it’s not a transformer. But the tensioning on a spring should be some kind of similar effect. But I think for the timer it must release the spring tension when it hits zero. Just guessing though.

Although most of us probably know about hysteresis from physics or the study of ferromagnetics, the general concept is one of a mechanism behaving differently depending on what state it’s currently in. From Wiki:

Yes. I meant that I didn’t know the exact definition of the term used in the mechanical sense. But I don’t think that definition applies to the timer mechanism as a whole.

I think of it as a matchbox tied to your finger with a piece of string, all on a table. At first, your finger and the matchbox are at the same position. If you move your finger a certain distance, the matchbox will move less because of the string. So the solution is to move your finger more, then back to the position you want.

I know that some timers will start (when unwound) before the zero, so that it might be on 55 minutes (for a 60 minute timer), so that there is some tension in the spring even if you set it to 0 minutes so it can ring the bell.