If a callsign is provided, QRZ is accessed to get the address for that callsign. Google is accessed to lookup that address and a latitude/longitude provided that is converted to a grid square.
If QRZ doesn't find the callsign, no lookup by callsign can be performed.
If QRZ has a different address for a callsign from what you'd expect, the address in QRZ is used. Should this program and QRZ contain different results for a grid square, both are displayed.
If Google can't find or pinpoint an entered address or the address taken from QRZ on a callsign search, a more generic location may be displayed and that location's grid square calculated.