I've got clocking errors on my NEAX 2400 MMG. In checking into this I found that the PBX does not have any connection to an external high stability oscillator, though there is such option in the documentation. I do have 4 T1's in the system which each are connected to the PLO for clocking adjustment. What is the function of an external high stability oscillator compared to the four T1? It appear that I can't have both the T1 and the external clocking source at the same time. Is that right? What should I aim to do to get a stable clocking of the system?