English: In the original Gulstad relay the line coils were not differentially wound; it could be used, therefore, only on Bridge duplex or simplex circuits. To utilize the advantages of the Gulstad principal on differential duplex circuits, the British Post Office has modified the Post Office standard relay, by adding extra windings and terminals. This modified instrument is known as a “G” relay and is equally suitable for differential or bridge duplex working. The internal and external connexions of this relay are shown in the figure, in which the dotted lines indicate the extra coils. For the correct reception of the incoming signals a Wheatstone receiver is connected to the relay tongue.