Sigma Metalytics Precious Metal Verifier Quick Start Manual page 13

Conditions that Affect Readings
Thin Samples
The sensor's signal may over-penetrate very thin samples and cause
inaccurate readings. Refer to the minimum thicknesses information
to make sure the sample meets the minimums for the sensor in use.
Place the calibration disk behind the sample and/or switch to a smaller
sensor if necessary.
Small Samples
It is important to use the correct sensor size for the sample size. If the
sample does not meet the minimum requirements for a sensor, the
device will not provide accurate readings.
Samples with High Relief
Samples with very deep stamping, molded samples with large designs,
and other high-relief samples may cause inaccurate readings. Try
to take a reading from a flat area of the sample to ensure the test is
accurate. Most coins and bars will not have this problem.
Bars
Some bars may only partially meet the minimum requirements for
the sensors. For example, a long, narrow bar may be longer than the
sensor minimum, but may not be wide enough for accurate testing. A
bar must meet the sensor minimums in width and length in order to be
accurately tested.
Cases
Cases made of plastic and/or cardboard should not affect the test
results. However, cases with metal in them will interfere with the testing
results.
Similarly, very thick cases may also cause the device to not read the
sample if the sample is too far away from the sensor. This is more
common in cases with a small or thin sample in a thick case. For
example, a 1/4 oz gold piece in a case that normally holds a 1 oz gold
piece may be difficult to read due to the case size.
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