If you are having trouble pinpointing...
 

This only is for locators where the transmitter is placed on the ground and you follow the signal line to the target. Think about a GPR sounding. The parabola shape is something like wind hitting the target--it spreads out laminar layers. So if you are downrange you will pick up all sorts of hits (usually a bit fuzzy) and they are all wide on both sides of the target. This is your clue that you went past the target, so you need to move back up range.