How reliable is the Fisch?
 

Fisch Wallet #2 says it can be used to test both 1 oz. Krugs, and 1 oz. Gold American Eagles.

But the composition of the coins is not the same. The 1 oz. Krug is 91.67% gold and 8.33% copper. The 1 oz. GAE is also a 22karat coin, except it is 91.67% gold, 3% silver, and 5.33% copper.

The specific gravities of copper and silver; Cu is 8.2 (grams/cm3), whereas Ag has a specific gravity of 10.5 (g/cm3).

Although both the Krug and GAE weigh in at a total of 1.0909 ounces, the differernt composition is reflected in a slightly thicker American Eagle. (The diameters of the coin are identical).

The Krugerrand is 2.75 mm thick, whereas the American Eagle is 2.87 mm thick. Stated differently, the GAE is .12 mm thicker than the Krugerrand, or around 4.36% larger by volume.

Since the Fisch balance will tip for both Krugs and GAEs, if you assume it is well engineered, the volumetric measure (i.e., slot), should be sized for the thicker of the two coins--and no more, i.e., the Fisch volume slot should be 2.87mm thick.

This in turn means that the Krug passes the thickness test on a Fisch, with an extra 4.36% diameter to spare (.12mm). Is this "margin or error" in the Fisch, worrisome? Why? Why not? (Note that all of the Fisch instruments that claim to test multiple coins, have this "margin of error" problem. My look at a coin spec table tells me that Panda's and Australian 1 ouncers could also be tested in the same instrument, although not the smaller coins. And Panda's and Kangaroos can't be tested at all in any Fisch, nor can Philharmonics)

Re: How reliable is the Fisch?
 

Something is amiss, since the GAE is alloyed with a mix of a higher average specific gravity that is the Krug, it should be denser and hence a slightly smaller volume. The specific gravity of a mix that is 36% silver and 64% copper should be close to 9.1.

Re: How reliable is the Fisch?
 

You're right, it doesnt make sense. Also, I misread the dimensions. The GAE is an all-around larger coin, despite having a heavier, blended specific gravity.

The Krug is 32.6mm diameter, and 2.75mm thick

The GAE is 34.3mm diameter, and 2.87mm thick.

Re: How reliable is the Fisch?
 

Fisch instruments work fine and last a long time. They're very reliable for what they are intended to check.

But be aware that a Fisch can not detect a counterfeit numismatic or other coin that is fabricated with the right metal (i.e. from melted metals from comparatively low cost legitimate same-type coins) and with the correct diameter and thickness.

Re: How reliable is the Fisch?
 

I've found that the GAE is a bit "tight" for the slot and the round depression on my Fisch but they do fit. I think this is because they were designed for the Krug only so it really is not for the GAE. Plus they are designed to allow for wear, manufacturing tolerances, etc and I don't think there is any metal you can subsutite into a GAE that will make the Fisch tip but still be a less valuable metal

Re: How reliable is the Fisch?
 

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