I have written a Chemical Bond Polarity Calculator application, which many students use for their homework. I sometimes get questions from these students as to why the cutoff I use is 2.0, and not some other number between 1.7 and 2.1. I understand that there is no hard and fast rule as to what the cutoff should be. I just want to know what a real chemist (I'm a computer programmer, not a chemist) would want this particular application to use for the cutoff. Conversely, would a real chemist want to be able to input the cutoff themselves?