Some users report seeing different results in NetSpot than in other WiFi-related apps. And we are here to officially announce that it is absolutely normal and will always be so. Even when other apps use the same Airport API, the signals change from second to second and there will always be some differences.
In fact, two apps running at the same time may easily influence each other. For that reason, we HIGHLY RECOMMEND that you disable any other software that might be working with your AirPort adapter while you are running a wireless survey with NetSpot.