Not sure I understand but I'll give it a shot.
The on time of a ground controlled actuator would be the time the signal spends low. (Duty Cycle neg) For example, to measure a ground controlled injector pulse width, you would place the rulers framing the time the injector voltage is low on the control side. This would include the peak section and the hold or pulse width modulation section, if any.
Keep in mind that often a higher frequency ground controlled solenoid waveform may appear as a sawtooth pattern, rather than a square wave, as a result of inductive reactance. Solenoids will also exhibit an inductive kick, which can be over a hundred volts, so be sure to use an attenuator when your not sure what this voltage might be.
THE PicoScope Automotive Authority
In North America