Michael W. Lynch
My "ZERO Line trace" stays flat, right against the bottom of the CRT graticule. When testing a transistor with the steps set to 1, I see two lines, the first is that "zero line trace" at the very bottom of the CRT and when increasing the collector voltage this line always moves straight across from left to right, with no perceptible vertical deflection. The next line or trace would be the single trace that you would expect to get. As the collector voltage knob is increased, that trace moves left and up from the corner of the graticule, as one would expect. Of course, this is indicating increased voltage as well as the presence of current. The ZERO line is always present , representing the collector voltage knob position, regardless of the number of steps selected, except when the collector voltage knob is set to zero; when it becomes a single dot. Hope this answers your question.