Well, more a matter of luck than science ....

First of all turn off the annoying beeping. My main applications were previously limestone walls and concrete floors, each with electric lines. Result: The position of electric lines can rather be presumed accurate and reliable localization I have never succeeded. Although the consumer is on (as described in manual), the machine usually respond only in the immediate vicinity of the switch or the lamp. Perhaps because there is closer the cable to the surface? Will you then the suspected wiring confirm a bit further away, you get displayed no electric but may metal. In concrete ceilings can you do with this info little.

The repeatability is abysmal. Several times driven on a line back and forth, the maximum deflection is never in the same place. The same is true if one goes a few centimeters in order to pursue the suspected line.

Conclusion: Better than nothing but it is always exciting when one sets the drill.