In the all numerical systems except the Roman numerical system.
The positional value is the value that takes a digit according to the position it occupies whitin the number ( units, tens, hundreds ...).
That is why the change of position of a digit within number alters the total value of it.
The number zero is used in all numerical systems. Is the numerical sign of null value, which in positional notation occupies the places where is no significant number. If it is located to the right of a number, its value is multiplied by 10. if is on the left, does not modify it.
In the roman numerical system the zero has no representation, it does not exist.
