Trouble is, I've personally seen 4 volts as an off-hook voltage! And 9 volts as an off-hook voltage. You are right though, current flow is what you want to monitor. And that can run from 15ma to 35ma off-hook!


When I was young, I was Liberal. As I aged and wised up, I became Conservative. Now that I'm old, I have settled on Curmudgeon.