A proposed name for a
dimensionless unit equal to the number
one, so that very large and very small numbers can be expressed using
standard SI prefixes. The symbol would be U. So you would write 3.7 nU for 3.7 x 10
-9.
The Consultative Committee for Units (CCU) proposed it in September 1998, and passed it on to the International Committee for Weights and Measures (CIPM), who accepted other CCU recommendations but decide not to pass this one on to the 1999 General Conference on Weights and Measures (CGPM), who do the actual adopting.
The CIPM asked the CCU to go away and ask some potential users. In 2004 they decided not to go ahead with the uno.
The need for such a symbol to denote numbers has come up before. An earlier proposal was the capital letter I. But as this clashes with the letter l for litre and the numeral 1, it was unsatisfactory. The numeral 1 itself was also proposed.