Thanks for the reply. I'm relatively new to electronics so I don't quite follow your suggestion;
If you know the supply voltage is stable, or you are using an external voltage regulator or the Arduino's regulator, you can measure the regulated supply with your DMM and not bother with the internal reference. Internal voltage ref can be very useful if the Arduino is powered by batteries and you are bypassing the voltage regulator to increase battery life for example.
If measuring such a small range of voltages using the ~5V supply as reference is not sufficiently accurate, you can use a voltage divider to scale down the voltage to be measured. You could do this with the internal reference also.
Are the above simply general characteristics of AREF?