Hi,
Post#1
I agree the graph doesn't make much sense.
There is Ohm's Law. R = V / I
And it says "constant voltage"
Let's calculate some values:
Let's assume V = 12V
Then: if
I = 1A --> R = 12 Ohms
I = 2A --> R = 6 Ohms
I = 4A --> R = 3 Ohms
I = 6A --> R = 2 Ohms
I = 12A --> R = 1 Ohms
You see: the higher the current, the lower the resistance.
This is what the graph shows.
Mind: the graph has no X values and no Y values. In most cases the axis are linear --> but there is no need for this.
Thus one may expect that the graph shows a hyperbola --> but there is no need for this. With non linear axis the graph may look like a straight line.
Post#3:
Both graphs show the correct relationship:
Constant R: the higher the current, the higher the voltage
Constant current: The higher R, the giher V.
Both are directly proportional. In both casess: with both linear axis you will get a straight line graph.
I recommend to do some example calculations and graphs with Excel to get a feel.
Klaus