Researching this machine I see one of the setting is for, 90% silver, pre 1945. While I imagine it works well on coins like the Morgans and Trade Dollars since they were struck at .900 silver. But what of the older silver coins. The dollars from 1795-1804 were .8924 silver. Would these have an accurate reading on the Sigma? Anyone use a Sigma on early US silver coins? I would like to get one, but if it doesn't work on my older coins, I'm not going to bother.