neper

Non-SI unit accepted for use with SI

Name	Symbol	Quantity	SI units
neper	Np	logarithmic ratio
The neper, symbol Np, is a non-SI unit accepted for use with the SI.   One neper, is equal to the neperian (or natural) logarithm of a ratio between two power quantities of 2:1, or the neperian (or natural) logarithm of a ratio between two root-power quantities of √2:1.

The neper is named after the Scottish mathematician John Napier (1550 – 1617), the inventor of logarithms.