AD627: Minimum Vref for single supplies.

Hi,

What is the minimum Vref for single supply configuration?

The following is figure 39 from the AD627's datasheet.

The minimum Vref curve is greater than 0V for Vin(-) <3.2V, but I can't find its exact value. Also, what happens if I force a 0V in Vref in that configuration?

Thank you