Subdelta Watches that are protected against magnetic fields make use of a weak iron movement-holder, weak iron dial and weak iron inner-caseback to protect the movement up to 1000 Gauss or 80.000 A/m.

Magnetism is one of the most frequent problems that affect the accuracy of mechanical watches.

A Soft iron inner case protects the movement against magnetic fields created by for instance Computers, Loudspeakers , Electric Motors and such.