When I set the horizontal axis to something large (40ms/div or greater) and hit the Single button, the scope triggers immediately, although no trigger event has occurred. I tried the following:
- Setting the trigger to something ridiculously high and grounding the channel that it triggers on, to make sure that noise was not triggering it. It still triggered immediately.
- Setting the horizontal scale to 20ms/div, hitting the Single button, and then increasing to 40ms/div. This worked; i.e. did not trigger until the trigger event actually occurred.
I am using a Tektronix MSO54, but I also recall observing this phenomenon on another scope in the past. This has got to be something obvious, but for the life of me I can't figure out what.