So I watched this extremely fundamental video about voltage measurement and how it's measured. The one thing that confuses me is what people use a reference for zero potential.
The two diagrams shown below have the exact configuration and order of batteries. The values don't change either. But I get two different values of net voltage based on where I assume the zero potential to be and this assumption is arbitrary. So if I choose the zero potential to be in the middle and if my friend chooses it to be at the end, we get two different voltages and we would both be right. So what does one do to avoid such ambiguity? Is there some pre set standard on how to measure voltage? And what does a manufacturer mean when he says a supply gives a 12V or 15V output? What would the manufacturer have used as a reference? For if I change the reference point, my voltage reading for the same supply would be different and this would have consequences, right?
Edit: So what I'm doing in the first diagram is, I first connect the red lead at the top to measure 12V. I then connect the red lead to the bottom to measure -12V, getting a net voltage of 0v.