What is wrong . Ohmeter or diode

That is because, the resistance of the diode that you've set at 1 Ohm, is the internal resistance of the diode. The Ohmmeter would have shown you 1 Ohm if there was a resistor of 1 Ohm instead of the diode. You see, the current that it is showing is calculated using a totally different formula. The current through a diode is calculated taking into consideration all its parameters. So, my main point is, that the overall resistance of the diode at 1 Volt (given by Ohmmeter) is 6.62 ohms. Note that the resistance of the diode changes as the voltage applied across it changes. Only its internal resistance is 1 Ohm.

@niranjan_23 : Parameter is called "ohmic resistance" and ohmeter source is DC voltage. So your explanation is not sufficient to me. However I tested DC source with diode and the result is : the higher is voltage, the closer 1 Ω is the ratio V/I.

Yes. That's what he is saying. The diode's Resistance gets lower as you put more voltage. It's exponential.

See what occurs when you play with the diodes saturation current while adjusting the voltage.

@BillyT : really weird because the saturation current concerns diode when it is reverse biased. Which is not the case here.

In fact, ohmeter works with internal DC voltage source 1V. For this voltage, current diode is 151 mA. So the equivalent resistance is 1/0.151=6.62 Ω