How accurate is AREF pin


I'm trying to make a milivoltmeter using my arduino Uno, for that I need to have a lower reference voltage than the default 5V so it can be more precise. So my question is: what is the minimum recognizable voltage for the AREF pin? Let's say I feed 10mv into the AREF pin, will it be able to recognize it? or it's too small that the arduino will just treat it as 0?

Thank you

According to the datasheet (hint), the minimum voltage on Vref is 1 V.

Thank You