I'm not in charge of handing out titles.
Worse, I'm an iconoclast.

 

Your a mind reader #12. That was my next question. Couldn't find a value for "input impedance" on the data sheet.

 

Simple enough. If input impedance is not described, play a bit with Ohm's Law. Find input bias current, resistance of the input signal path, and IR is the error voltage produced by the input circuit.

That's how input bias CURRENT works. Input offset VOLTAGE is added to those results in a +/- way.