Using external analog reference

I'm a little unclear on the results this would generate. Right now I read voltage on two analog pins and subtract the smallest from the largest to get the difference. If I were to take one of those inputs and use it as an external reference, would the analog read result be the same as if I did the math/ For instance...

A0 = 500
A1 = 600
End Result = 600 - 500 = 100

Would this produce the same results?

AREF = 500
A1 = 600

Because the reference is 500, would the read on A1 produce 100?

Thanks

No, AREF sets the upper limit. And you cannot use any voltage is has to be within some limits (as far as I remember the datasheet 1.5V to Vcc).

The data sheet says 0-5V for the AREF. What I'm wondering is if I put 2.5V on AREF, then put 3V on A0, what will an analog read show? Then go the other way and put 2V on A0, what will it show?

Using a 5V ref, 0-5V on A0 reads the actual voltage (0-5V) Just wondering if I use a different AREF if that will offset the analog read result.

What I'm wondering is if I put 2.5V on AREF, then put 3V on A0, what will an analog read show?

1023

Then go the other way and put 2V on A0, what will it show?

About 820.