As a further security measure, if the first attempt to set up a path to a register failed, so that, on an outgoing call, the customer did not get dial-tone, the exchange recognised the failure, stored the details of the equipment in use on the failed call and automatically made a second attempt, using different equipment. This happened so quickly (about 50 milliseconds) that, if the second attempt was successful, the customer would not have been aware of the failed first attempt to get dial-tone.