Incorrect.
V = I*R. If R is constant (i.e. simple fixed resistor), V increases as I increases.
For anyone that cares, go to the chart referenced, calculate R = V/I at several values of I and plot the curve. You should see R decrease with I for the diode. I only mentioned the behavior in terms of resistance because I thought it would help the explanation, not to confuse people. The diode acts as a variable resistor that conducts little at lower currents and opens a path around the ammeter at higher currents. Bottom line is, it works for me and should help anyone who wants to up their alternator and keep their ammeter. But I don't recommend trying your own design unless you are skilled in basic electronics and algebra.