> A PRS10 with a long shelf life will need more than 10 months (not days !) to > get its final drift. Its dépends of the homogeneity of the gas mixture > (Rb85,87 and krypton) in the cell and a long non running time affects the > mixture. What's going on there? Why/how does the mixture change? How does the mixture effect the frequency? If that is significant, how do they make the mixture at the factory accurately enough? Or is it small so they just tune around it? -- These are my opinions. I hate spam.