Reading and Interpreting Tolerances

In addition, some sources of error really are constant and don't change with the reading. In the case of small DC voltages, some errors are due to thermoelectric effects in internal connections and are not related to the displayed measurement value.

In order to prevent specifying tolerances of zero, and to properly take constant errors into account, we specify a term proportional to the Range.

This is known as the "floor spec."

Example

1-year accuracy of the 3458A for DC voltage on the 1V range without Option 002 = 8 ppm of reading + 0.3µV

8 ppm is the proportional term.

+ 0.3µV is the floor spec.

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