I remember this very old riddle involving lateral thinking. I was surprised that I cannot find it here. (Or maybe did I use wrong keywords? If so, please mark as duplicate)
Girl is looking at an object.
During the flow of the time, it is becoming thinner at one side and thicker at another. What is she looking at?
In addition, it has multiple solutions. Can you guess them all? I will give some hints.
Is today classic (and at the same time it is the most exact solution).
Is today vintage.
Is today medieval technology (or even possibly neolithic).
2 and 3 can be difficult because nowadays, most of young people have never seen such devices. Luckily 1 is still in use today.
*4. Writing this, I just noticed another solution on my screen.
As many people post very good solutions I noticed that I should be more specific:
1 and 2 are kinds of medium.
3 is a tool.
4 can be a part of UI component
I just removed unnecessary history from the question
Congratulations to xhienne and FLash.