why is this so stationary? I had worked with real oscilloscopes, and it's always tricky to get a steady picture, especially on the old analog ones. But here, no

why is this so stationary? I had worked with real oscilloscopes, and it's always tricky to get a steady picture, especially on the old analog ones. But here, no matter what I do, the picture is rock solid. Two slightly detuned generators added up? Somehow beat frequency does not appear. Mess with trigger? Real scope would either switch to "auto" mode with wildly changing signal or have picture disappear entirely. Here, it's basically no effect.