Hello, I am a new subscriber to the list ! I am located in France and I play with time and frequency instruments on my free time. Recently I've bought an used FS725 unit with a PRS10 oscillator in it. I was wondering how can I estimated the age of the Rubidium oscillator. I think the age is related to the lamp voltage but which voltage should I read ? In the documentation, there are a lot of parameters, for example AD3 : Drain voltage to lamp FET / 10 AD4 : Gate voltage to lamp FET / 10 Which one is related to the lamp aging and what are the standard values for a new oscillator ? I have an LPRO oscillator and with it I can measure easily the voltage directly. A new unit is at about 15V and it decrease slowly (about 20 mV/month). Thanks! jps