I have a couple of Betax #4 shutters. The best one appears to fire accurately at all speeds, although I don't have a shutter tester. All your shutter speeds are within half a stop in accuracy, except 1/50. If the shutter has been heavily used, that is as good as it's going to get. IMO, you have a very usable shutter. If you need greater accuracy, you might look into a professionally CLA's Compur or Copal.