How can they determine who is correct satisfying the above conditions?

Question

There is a barrel with no lid and some wine in it.

“This barrel of wine is more than half full”, says Mark.

“No, it’s not”, says Steve. “It’s less than half full.”

They do not have any measuring instruments with them.

They cannot remove any wine from the Barrel

How can they determine who is correct satisfying the above conditions?

Answer 1

Hold the barrel at an angle.
If the barrel is half full the wine will go from one end to the exact opposite (in all 3 dimensions).
If the wine level is lower, the barrel is less full. If the wine level is higher, the barrel is more than half full.