Data derived from the oscilloscope may sometimes cause confusion, particularly if you do not take the zero line into account. Thus it is possible to manipulate two diagrammes of different measurements by various settings in such a way that they correspond to one other. If you are working with an oscilloscope, one that is also used by electronic engineers, one signal can be deducted from another signal by 'Inverting' or changing poles and shifting in Y direction.
How it works
The data above stem from two different injection signals. If you want to find out how such a signal looks like in a wider context, please click here.
How do these signals come about? The figures 2 and 4 display the corresponding circuit. The signal shown in figure 1 develops from the voltage drop between the measures of the ground rated output of the control device to the injector and terminal 15 (12 V). Figure 3 develops by connecting instead of terminal 15 ground to the multimeter.You do not need to argue which signal is correct, because this is valid for both. The indicated injection pulse timing is the same in both cases. The question would rather be which signal is more common in the workplace practise. This question is also unambiguously. The signal displayed in figure 1 can be received at both connections of an injector. But there are a lot of testers (e.g., Gutmann) which can display the signal only in the form of figure 2. This signal also dominates in the technical literature. You may not act as described above, making adjustments in such a way as if you would have measured at another place.Of course the signal can only be gained in this form if you do not disconnect the respective injector.
Dir. Petrol Injection 1
Petrol Injection Signal 
