Drew and ska are half right. You really need to learn how your machine reacts. But you can't know for sure every time as some large iron will ring up as coins. Location plays a part, too. The house I hit tues was from 1760. The fact the yard ended where there is a parking lot for a plaza with a liquor store is why there were so many empty cans and small bottle tops. The fact the house was a repo is the reason why all the other junk was there. Even the cellar hole I went to with an admin, del, had plenty of iron. I couldn't walk 3 ft without getting a quick false from iron. I even found a brand new nut. Probably fell off a bolt of something like a chain saw or other small equipment as they were cutting down trees. And the age of houses listed on an assessors site can be inaccurate. Two houses on my map from 1868 are neighbors. Obvi the houses existed on the lots before the map was drawn. One has the stone foundation which is much older than 1900, however assessors site has it listed built 1900. Maybe it was rebuilt in 1900 due to a fire. Research the property (if you can). The age of the property can tell you how old coins and relics can be found there. And as even said in my manual, junk like cans can ring up like coins. A washer or ring terminal sure rang up like a coin for me. Digging junk is almost unavoidable. Keep swinging the coil and don't get discouraged with finding junk. After digging almost 11 pieces of junk I stumble on one good find...