Hello Forrest, Your question regarding prolonging cesium tube life is very valid and has several answers depending on the particular situation. I can remember asking exactly the same question to the list many years ago. For the 5061A/B the answer is relatively simple. There is a 'Cs Off' switch position that turns every thing to the tube off except the vac-ion pump. This does not shorten the tube life in any way, and keeps the unit ready to use (after the Cs oven warm-up time). The downside is that you are burning power continuously to keep all the other circuitry powered. It still may take a week or so for the unit to reach its ultimate stability. Another alternative is to keep the unit powered off and just turn it on ever now and then to keep the tube pumped down, as Taka has suggested. I have a Datum PRS-50 that I treat this way (there is no way to just maintain the vac-ion pump). Another option is to keep the unit in storage and only power on when needed. This can take considerable time to pump down the tube depending on how 'leaky' it is and how much Cs is floating around inside. Some units I have seen pump down within minutes/hours, others may take weeks (and I have even had them work afterwards). Of course, once you get the unit locked it still may take a considerable time to reach thermal equilibrium and its ultimate stability. Bottom line is - if the Cs oven is running, so is the clock on your tube. Regards, Skip Withrow