I was using it on my iphone today ( on the train
) , and it did tell me when the gps signal was good, poor or non existant..Top left corner green, yellow or red light. It also let me know what kind of error I could have been experiencing in metres.
It didnt go that well in the train, but have been playing with it (obsessively) since i downloaded it, and its been pretty accurate everywhere else. I can only assume the overhead wires were not being all that friendly to the signal?.