Contact refers to the contact blades making up a Reed Switch or Electromechanical Relay. The contact configuration used for a given design or application is typically described by its contact form such as 1 Form A, 1 Form B, etc. Contact, Form A is a single pole single throw (SPST) normally open (N.O.) switch. Contact, Form B is a single pole single throw (SPST) normally closed (N.C.) switch. Contact, Form E is a bistable contact that can exist in either the normally open or normally closed state such as in a latching relay or sensor. Reversing the magnetic field causes the contacts to change their state.