Set it to 6 to start off with (no attennuation), then when you move the dish and it finds a satellite the tone will sound or the needle will deflect, probably to full scale. When it does this, turn it a little in the other direction, until the needle is in the middle, then try tweaking the dish again. This facility is so that you can zero in on both high and low power satellites, try and keep it in the middle of the scale by adjusting the attennuation until you can get no more increase in signal from either horizontal or vertical dish movement.