I've used testers when I was an electrician to see if a wire was hot or not, but it didn't tell me anything else. Wiring is different for different cases, so I'm curious what exactly you were measuring.
Discussion
An EMF meter.
That field is impacted by amount of current though, which can be different for different wires/devices. What were you comparing against? I'm curious as to how you determined one thing to be good or bad compared to another.
Simple, less is better. And there are safety standards. My device starts beeping when it gets over the safety standard.