I'll add a little to what doozis provided with a couple more quotes from some previous posts and a link that shows a diagram as to how and when a coin rings as it passes under the coil. It's very important to understand where and when the coin sounds as the coil passes over it because this is the only way that you can narrow down the location of the coin/object, and that is very important. With a 150, it is mandatory and the only way to PP. Being able to narrow down the location of the object without the use of the PP'er is the first step in learning to PP accurately. Avoid looking at the bars, avoid the move the coil forward & back technique they show on the DVD.......you don't want to use that length of the coil to PP. Avoid shortcut standards that say the coin will be on this part of the coil. Simply think about the center of the coil where that little U is as your mental eye will do the rest as you gain experience.
Number #2 is to understand how targets sound off under the coil, because it doesn't happen in the center of the coil.........read this.....it might save you from digging a manhole and will be crucial to learning how to do some primary X'ing of the target before you start using the PP'er....
http://www.garrett.com/hobby/techsupport/pinpointing.htm# Select the Manually Locating a Target (ACE 150) for a visual demo of how targets sound off under the coil.
This was in response to a hand held PP'er
Is a PP'er necessary? In my opinion, no. Give yourself a little time to learn the 250 and you will be fine. It's all in trial and error, and each and every time you go out there, you will bring back with you something new learned, to the point where you will feel like an expert at some point or another, but no matter how many times you go out there, you will learn something new. My advice in learning to PP with the 250 is simple, first, forget about the PP'er altogether. Try to get as precise an idea of where the object/coin is just by sweeping the coil over. Keep in mind that the machine rings off not in the center, but the outer coils. This would apply even more for a 150 without the PP. Believe it or not, if you get good at this method, you can PP with relative accuracy on that alone. Once that is put into practice, start getting good on the PP'er. My absolute advise for PP'ing with the 250 is do not even try looking at the screens bars. You will loose yourself. Do not even try to concentrate on a certain spot on the coil. Simply focus on the center of the coil and where it sounds the loudest as you pass it over the target. Although standard to change the X angle by sweeping forward and backward, I strongly advise against it and instead recommend you turn your body 90 degrees at give it another sweep. Listen, the advise me or anyone here can give you does not make up for actual hands on practice, so get out there and put some hours into learning your machine. It's no science and you will pick up its behavior.
Best,
Ricardo
