Time Nuts- Usually the output of my TSC5110A and TSC5120A analyzers looks like you would expect - a random walk. Occasionally, I get a much more structured phase pattern, like this one, from a TSC5110A. The period of quasi-periodic pattern is 16 sec in this case. Again, the instrument normally produces a typical-looking random walk pattern. With some pairs of DUT oscillators, the output looks like this instead, when you zoom in a look closely. Does anyone have a plausible explanation for this type of pattern? Thanks- Jim Emacs! Emacs! Emacs!