'Is on screen' refers to a position. Is the position on the screen or not.
I know that the SliderBar has no 'Is visible' condition. It is a form element. So .....
Give SliderBar an instance Boolean 'VisBle', set it to true (in the properties ... if it starts visible)
Now the code is:
(SliderBar) Is Boolean set ('VisBle')
__________________set Boolean ('VisBle') to false
__________________set Boolean ('VisBle') to true
Else is NEEDED, else the first event (set invisible) will set the second event ALWAYS true.