Calculated resistance of an LED
Well, you're on your way to finding out that the resistance of a diode is not linear!  But you have the right equipment and know the right formula R = V / I (ohms law).  Measure the voltage and the current and then calculate the resistance of the LED.  You will find that it changes!  

Remember - if you replaced the LED with a fixed resistor at that calculated value, you should get the same current and voltage reading.