Personality who deals with a 10,000 telephone calls a day is "TIM" - The Post office Speaking Clock. Since the service started in 1936 over 515 million calls have heard the golden voice say...."on the third stroke the time will be ...." The voice heard after dialling "TIM" is a reproduction of a recording made by Miss Jane Cain twenty years ago. The principle of reproduction is similar to that used in films, but the sound track is hermetically sealed on concentric rings in four glass discs . The clock is accurate fo 1/10th of a second. Photo shows: The Post Office invited the press to view "TIM" , housed in the Hoborn Telephone Exchange. In this picture technical officer William McGoun shows two girl visitors the recorded mechanism ofthe clock .