A new SI unit for any logarithmic quantity. It is equal to the number one, and scales by natural logarithms. The symbol is Np.

What I think that means is that a value of 2 Np is e times bigger than one of 1 Np, and 3 Np is e times bigger than 2 Np, and so on.

Neper is an alternative spelling of Napier: it was named after John Napier or John Neper, the Scottish inventor of natural logarithms.

Quantities that can be measured in nepers are field level, power level, and logarithmic decrement -- whatever they are. It is important to specify the reference level, because these are not absolute magnitudes but scalars.

The unit and name were agreed on by the CIPM (International Committee for Weights and Measures) in 1998 to be presented to the 21st CGPM (General Conference) in 1999. I have not been able to locate confirmation that the CGPM accepted them, but normally I think with CIPM acceptance it's a shoo-in.

At the same time they were to adopt the existing unit bel, a decimal logarithm, as an SI unit.

SI unit for the ratio of two numbers expressed using a natural logarithm formula:

For two scalar values a and b, the value of Np is ln(a/b)/2

1 Np is equal to a ratio of e2 (I am not making this up!) or about 7.4 and corresponds to approximately 8.7dB. -1 Np is about 0.135 (1/e2). A decibel is 10 log(a/b)

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