I use a 1M/470k divider circuit, which will reduce 3.44V down to 1.1V, and then use the 1.1V internal voltage reference. This is perfect for my uses because I don’t use voltages over 3.44V. Of course, if you do, you’ll want a larger divider. In my case, when analogRead(A3) returns 1024, I have 3.44V. In the sensornet example it works like this: