Its really easy. Example measure the voltage. Is it 48v, 36v or 24v? Then set your varc to whatever you measured. This is just an example. Regarding B-answer or if clear signal is available, you need a volt meter. Example, you will test 1 analog trunk line, connect an analog telephone set at your end and also parallel connect a volt meter. Digital volt meter is better but analog meter should be okay. Lift the handset, you will see that the voltage drops but polarity is the same. Dials the number you require and if someone answer, did the polarity change? That how easy it is. Then you can set your parameter according to your b-answer result. Then check carefully the polarity and ask the other end to hangup. Is polarity change when B party hangup. Then set your parameter to whatever your findings. Its easy.... If you need to change the characteristics of the line, then you need to request it who ever provide this line.