Abstract: Data transmission test set used for making error counts and incorporating a new and improved synchronization detector to rapidly detect loss of synchronization between the received data pattern which is supposed to be a psuedo random pattern and the locally generated error free replica psuedo random test pattern. In this system, the received data pattern and a first locally generated psuedo random pattern are used to generate an error pattern which is then used to effect generation of a second local psuedo random comparator pattern.The second pattern and the error pattern are then used to generate a third pattern, the bits of whichare used to determine if loss of synchronization has or has not occurred. Loss of synchronization is determined almost immediately thus preventing the running error count from being severely affected by loss of synchronization. The detected occurrence of loss of synchronization is used to resync the test set and is also displayed to the test set user.