I realize that the metal detector was probably not designed around US coins. The zinc penny usually bounces between two zones the low and high conductor zone. Which makes for two different tones if you are setup like that. It would be nice if they hit a few numbers higher like 23. This way you could set one tone for low conductors and one for higher conductors. There is not a lot ID numbers between a nickel and a zinc penny. Nickels hit at 13 and zinc about 20-21. Corroded zincs will hit lower and 3 ring civil war bullets hit at 19 or lower. This only leaves ID's 14-17 to cover all the aluminum trash targets. The ID is pretty stable so that helps.