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<p>[QUOTE=&quot;-jeffB, post: 2786053, member: 27832&quot;]Bingo. The resistance of a silver coin will be somewhere in the micro-ohm range. That means that if you push a full amp through the coin, you&#039;ll be trying to accurately measure a voltage drop of microvolts, which is <i>extremely</i> challenging (read &quot;expensive&quot;).</p><p><br /></p><p>The real killer, though, is contact resistance. There&#039;s no way you&#039;ll reduce that below the coin&#039;s own resistance without plating or soldering large contacts directly onto the coin&#039;s metal. Even driving a spike into the coin probably wouldn&#039;t be good enough.</p><p><br /></p><p>Actual electrical testers work by <i>inducing</i> current in the coin (like a transformer) and measuring the induced current&#039;s behavior. I&#039;m still skeptical about those testers being reliable in practice, but they&#039;re apparently good enough, or at least convincing enough, to maintain a market.[/QUOTE]</p><p><br /></p>

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