Schedule Board / counting machine

Sometimes when we are going to decide a period of time
which is available for all the members
to have a meeting or discussion,
We’ll find it’s difficult to collect everyone’s schedule.One Schedule Board can solve this problem well.
First write down the possible time on the writing board.
Then one just presses down the button if that period of time
is not available for him,
and pass the Schedule Board to the next person.
Of course, if the button has already been pressed down,
the next person don’t need to press it again.
Finally the buttons which are not pressed
shows that the corresponding time is OK for everyone.