I'm seeing jumps in the frequency from a crystal, and a while later, jumps back to the previous frequency. (or as close to it as I can measure) I get roughly 1 a month. The jump is about 0.2 PPB. The crystal is inside an HP 5234B with option 010, the high stability oven oscillator. Has anybody seen anything like this before? Is there a term for it? What should I look for? ... Graphs and such for 4 examples: https://www.glypnod.com/TimeNuts/jump/jump.html 18 hours, 2 hours, 1/2 hour, and 10 minutes. -- These are my opinions. I hate spam.