Anti-magnetic shields - question

Possibly a stupid question...

Some watches have an antimagnetic shield inside, but when watches have a display caseback, they don't... or do those models have another kind of antimagnetic protection?

Is the antimagnetic shield required?

Thanks

Dan

If there's a caseback and you can see the movement then it lacks magnetic shielding. The traditional way of providing shielding would be with an iron casing, for example. However some movements make use of amagnetic materials for parts that are prone to affect timekeeping were they to be magnetised such as the hairspring being made of silicon.

Thanks