Foil to nickle bounce ... if you are getting a low tone that bounces to mid-tone which is foil or a high tone nickle ID, dig. Some low tone to high tone bounces are iron signals. If you slow the sweep way down, they normally stay low tone iron signals. If they are big iron targets, going to auto-tune (all metal) or use the pinpoint, you can size the target. If it is big and gives a low or a low to high tone bounce, I frequently walk away from it. I will dig virtually every target that gives a low tone to mid-tone bounce. Have recovered several small gold rings and small gold pendants by digging those signals.
Here is one from a while ago: http://www.findmall.com/read.php?23,1675537,1675537#msg-1675537
edited to add: If it is a deep low tone target that pinpoints as a small target, it can pay to dig. I have not found a ring that way yet, but there is a post somewhere on the forum where testing showed a deep ring that a CZ found, registered as low tone. Other detectors that were being used to compare signals were not seeing the ring until the ring was pulled up not quiet so deep.